![Jeff Layton](/assets/img/avatar_default.png)
The following set of operations on a NFS client and server will cause server# mkdir a client# cd a server# mv a a.bak client# sleep 30 # (or whatever the dir attrcache timeout is) client# stat . stat: cannot stat `.': Stale NFS file handle Obviously, we should not be getting an ESTALE error back there since the inode still exists on the server. The problem is that the lookup code will call d_revalidate on the dentry that "." refers to, because NFS has FS_REVAL_DOT set. nfs_lookup_revalidate will see that the parent directory has changed and will try to reverify the dentry by redoing a LOOKUP. That of course fails, so the lookup code returns ESTALE. The problem here is that d_revalidate is really a bad fit for this case. What we really want to know at this point is whether the inode is still good or not, but we don't really care what name it goes by or whether the dcache is still valid. Add a new d_op->d_weak_revalidate operation and have complete_walk call that instead of d_revalidate. The intent there is to allow for a "weaker" d_revalidate that just checks to see whether the inode is still good. This is also gives us an opportunity to kill off the FS_REVAL_DOT special casing. [AV: changed method name, added note in porting, fixed confusion re having it possibly called from RCU mode (it won't be)] Cc: NeilBrown <neilb@suse.de> Signed-off-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
543 lines
22 KiB
Plaintext
543 lines
22 KiB
Plaintext
The text below describes the locking rules for VFS-related methods.
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It is (believed to be) up-to-date. *Please*, if you change anything in
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prototypes or locking protocols - update this file. And update the relevant
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instances in the tree, don't leave that to maintainers of filesystems/devices/
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etc. At the very least, put the list of dubious cases in the end of this file.
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Don't turn it into log - maintainers of out-of-the-tree code are supposed to
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be able to use diff(1).
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Thing currently missing here: socket operations. Alexey?
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--------------------------- dentry_operations --------------------------
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prototypes:
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int (*d_revalidate)(struct dentry *, unsigned int);
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int (*d_weak_revalidate)(struct dentry *, unsigned int);
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int (*d_hash)(const struct dentry *, const struct inode *,
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struct qstr *);
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int (*d_compare)(const struct dentry *, const struct inode *,
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const struct dentry *, const struct inode *,
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unsigned int, const char *, const struct qstr *);
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int (*d_delete)(struct dentry *);
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void (*d_release)(struct dentry *);
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void (*d_iput)(struct dentry *, struct inode *);
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char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
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struct vfsmount *(*d_automount)(struct path *path);
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int (*d_manage)(struct dentry *, bool);
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locking rules:
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rename_lock ->d_lock may block rcu-walk
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d_revalidate: no no yes (ref-walk) maybe
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d_weak_revalidate:no no yes no
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d_hash no no no maybe
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d_compare: yes no no maybe
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d_delete: no yes no no
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d_release: no no yes no
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d_prune: no yes no no
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d_iput: no no yes no
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d_dname: no no no no
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d_automount: no no yes no
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d_manage: no no yes (ref-walk) maybe
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--------------------------- inode_operations ---------------------------
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prototypes:
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int (*create) (struct inode *,struct dentry *,umode_t, bool);
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struct dentry * (*lookup) (struct inode *,struct dentry *, unsigned int);
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int (*link) (struct dentry *,struct inode *,struct dentry *);
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int (*unlink) (struct inode *,struct dentry *);
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int (*symlink) (struct inode *,struct dentry *,const char *);
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int (*mkdir) (struct inode *,struct dentry *,umode_t);
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int (*rmdir) (struct inode *,struct dentry *);
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int (*mknod) (struct inode *,struct dentry *,umode_t,dev_t);
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int (*rename) (struct inode *, struct dentry *,
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struct inode *, struct dentry *);
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int (*readlink) (struct dentry *, char __user *,int);
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void * (*follow_link) (struct dentry *, struct nameidata *);
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void (*put_link) (struct dentry *, struct nameidata *, void *);
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void (*truncate) (struct inode *);
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int (*permission) (struct inode *, int, unsigned int);
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int (*get_acl)(struct inode *, int);
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int (*setattr) (struct dentry *, struct iattr *);
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int (*getattr) (struct vfsmount *, struct dentry *, struct kstat *);
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int (*setxattr) (struct dentry *, const char *,const void *,size_t,int);
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ssize_t (*getxattr) (struct dentry *, const char *, void *, size_t);
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ssize_t (*listxattr) (struct dentry *, char *, size_t);
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int (*removexattr) (struct dentry *, const char *);
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int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
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void (*update_time)(struct inode *, struct timespec *, int);
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int (*atomic_open)(struct inode *, struct dentry *,
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struct file *, unsigned open_flag,
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umode_t create_mode, int *opened);
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locking rules:
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all may block
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i_mutex(inode)
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lookup: yes
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create: yes
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link: yes (both)
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mknod: yes
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symlink: yes
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mkdir: yes
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unlink: yes (both)
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rmdir: yes (both) (see below)
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rename: yes (all) (see below)
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readlink: no
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follow_link: no
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put_link: no
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setattr: yes
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permission: no (may not block if called in rcu-walk mode)
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get_acl: no
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getattr: no
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setxattr: yes
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getxattr: no
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listxattr: no
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removexattr: yes
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fiemap: no
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update_time: no
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atomic_open: yes
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Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
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victim.
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cross-directory ->rename() has (per-superblock) ->s_vfs_rename_sem.
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See Documentation/filesystems/directory-locking for more detailed discussion
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of the locking scheme for directory operations.
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--------------------------- super_operations ---------------------------
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prototypes:
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struct inode *(*alloc_inode)(struct super_block *sb);
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void (*destroy_inode)(struct inode *);
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void (*dirty_inode) (struct inode *, int flags);
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int (*write_inode) (struct inode *, struct writeback_control *wbc);
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int (*drop_inode) (struct inode *);
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void (*evict_inode) (struct inode *);
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void (*put_super) (struct super_block *);
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int (*sync_fs)(struct super_block *sb, int wait);
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int (*freeze_fs) (struct super_block *);
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int (*unfreeze_fs) (struct super_block *);
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int (*statfs) (struct dentry *, struct kstatfs *);
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int (*remount_fs) (struct super_block *, int *, char *);
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void (*umount_begin) (struct super_block *);
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int (*show_options)(struct seq_file *, struct dentry *);
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ssize_t (*quota_read)(struct super_block *, int, char *, size_t, loff_t);
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ssize_t (*quota_write)(struct super_block *, int, const char *, size_t, loff_t);
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int (*bdev_try_to_free_page)(struct super_block*, struct page*, gfp_t);
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locking rules:
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All may block [not true, see below]
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s_umount
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alloc_inode:
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destroy_inode:
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dirty_inode:
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write_inode:
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drop_inode: !!!inode->i_lock!!!
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evict_inode:
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put_super: write
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sync_fs: read
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freeze_fs: write
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unfreeze_fs: write
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statfs: maybe(read) (see below)
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remount_fs: write
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umount_begin: no
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show_options: no (namespace_sem)
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quota_read: no (see below)
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quota_write: no (see below)
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bdev_try_to_free_page: no (see below)
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->statfs() has s_umount (shared) when called by ustat(2) (native or
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compat), but that's an accident of bad API; s_umount is used to pin
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the superblock down when we only have dev_t given us by userland to
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identify the superblock. Everything else (statfs(), fstatfs(), etc.)
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doesn't hold it when calling ->statfs() - superblock is pinned down
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by resolving the pathname passed to syscall.
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->quota_read() and ->quota_write() functions are both guaranteed to
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be the only ones operating on the quota file by the quota code (via
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dqio_sem) (unless an admin really wants to screw up something and
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writes to quota files with quotas on). For other details about locking
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see also dquot_operations section.
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->bdev_try_to_free_page is called from the ->releasepage handler of
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the block device inode. See there for more details.
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--------------------------- file_system_type ---------------------------
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prototypes:
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int (*get_sb) (struct file_system_type *, int,
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const char *, void *, struct vfsmount *);
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struct dentry *(*mount) (struct file_system_type *, int,
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const char *, void *);
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void (*kill_sb) (struct super_block *);
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locking rules:
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may block
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mount yes
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kill_sb yes
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->mount() returns ERR_PTR or the root dentry; its superblock should be locked
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on return.
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->kill_sb() takes a write-locked superblock, does all shutdown work on it,
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unlocks and drops the reference.
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--------------------------- address_space_operations --------------------------
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prototypes:
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int (*writepage)(struct page *page, struct writeback_control *wbc);
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int (*readpage)(struct file *, struct page *);
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int (*sync_page)(struct page *);
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int (*writepages)(struct address_space *, struct writeback_control *);
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int (*set_page_dirty)(struct page *page);
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int (*readpages)(struct file *filp, struct address_space *mapping,
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struct list_head *pages, unsigned nr_pages);
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int (*write_begin)(struct file *, struct address_space *mapping,
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loff_t pos, unsigned len, unsigned flags,
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struct page **pagep, void **fsdata);
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int (*write_end)(struct file *, struct address_space *mapping,
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loff_t pos, unsigned len, unsigned copied,
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struct page *page, void *fsdata);
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sector_t (*bmap)(struct address_space *, sector_t);
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int (*invalidatepage) (struct page *, unsigned long);
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int (*releasepage) (struct page *, int);
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void (*freepage)(struct page *);
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int (*direct_IO)(int, struct kiocb *, const struct iovec *iov,
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loff_t offset, unsigned long nr_segs);
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int (*get_xip_mem)(struct address_space *, pgoff_t, int, void **,
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unsigned long *);
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int (*migratepage)(struct address_space *, struct page *, struct page *);
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int (*launder_page)(struct page *);
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int (*is_partially_uptodate)(struct page *, read_descriptor_t *, unsigned long);
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int (*error_remove_page)(struct address_space *, struct page *);
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int (*swap_activate)(struct file *);
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int (*swap_deactivate)(struct file *);
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locking rules:
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All except set_page_dirty and freepage may block
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PageLocked(page) i_mutex
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writepage: yes, unlocks (see below)
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readpage: yes, unlocks
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sync_page: maybe
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writepages:
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set_page_dirty no
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readpages:
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write_begin: locks the page yes
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write_end: yes, unlocks yes
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bmap:
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invalidatepage: yes
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releasepage: yes
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freepage: yes
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direct_IO:
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get_xip_mem: maybe
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migratepage: yes (both)
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launder_page: yes
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is_partially_uptodate: yes
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error_remove_page: yes
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swap_activate: no
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swap_deactivate: no
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->write_begin(), ->write_end(), ->sync_page() and ->readpage()
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may be called from the request handler (/dev/loop).
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->readpage() unlocks the page, either synchronously or via I/O
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completion.
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->readpages() populates the pagecache with the passed pages and starts
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I/O against them. They come unlocked upon I/O completion.
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->writepage() is used for two purposes: for "memory cleansing" and for
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"sync". These are quite different operations and the behaviour may differ
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depending upon the mode.
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If writepage is called for sync (wbc->sync_mode != WBC_SYNC_NONE) then
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it *must* start I/O against the page, even if that would involve
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blocking on in-progress I/O.
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If writepage is called for memory cleansing (sync_mode ==
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WBC_SYNC_NONE) then its role is to get as much writeout underway as
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possible. So writepage should try to avoid blocking against
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currently-in-progress I/O.
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If the filesystem is not called for "sync" and it determines that it
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would need to block against in-progress I/O to be able to start new I/O
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against the page the filesystem should redirty the page with
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redirty_page_for_writepage(), then unlock the page and return zero.
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This may also be done to avoid internal deadlocks, but rarely.
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If the filesystem is called for sync then it must wait on any
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in-progress I/O and then start new I/O.
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The filesystem should unlock the page synchronously, before returning to the
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caller, unless ->writepage() returns special WRITEPAGE_ACTIVATE
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value. WRITEPAGE_ACTIVATE means that page cannot really be written out
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currently, and VM should stop calling ->writepage() on this page for some
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time. VM does this by moving page to the head of the active list, hence the
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name.
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Unless the filesystem is going to redirty_page_for_writepage(), unlock the page
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and return zero, writepage *must* run set_page_writeback() against the page,
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followed by unlocking it. Once set_page_writeback() has been run against the
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page, write I/O can be submitted and the write I/O completion handler must run
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end_page_writeback() once the I/O is complete. If no I/O is submitted, the
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filesystem must run end_page_writeback() against the page before returning from
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writepage.
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That is: after 2.5.12, pages which are under writeout are *not* locked. Note,
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if the filesystem needs the page to be locked during writeout, that is ok, too,
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the page is allowed to be unlocked at any point in time between the calls to
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set_page_writeback() and end_page_writeback().
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Note, failure to run either redirty_page_for_writepage() or the combination of
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set_page_writeback()/end_page_writeback() on a page submitted to writepage
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will leave the page itself marked clean but it will be tagged as dirty in the
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radix tree. This incoherency can lead to all sorts of hard-to-debug problems
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in the filesystem like having dirty inodes at umount and losing written data.
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->sync_page() locking rules are not well-defined - usually it is called
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with lock on page, but that is not guaranteed. Considering the currently
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existing instances of this method ->sync_page() itself doesn't look
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well-defined...
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->writepages() is used for periodic writeback and for syscall-initiated
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sync operations. The address_space should start I/O against at least
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*nr_to_write pages. *nr_to_write must be decremented for each page which is
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written. The address_space implementation may write more (or less) pages
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than *nr_to_write asks for, but it should try to be reasonably close. If
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nr_to_write is NULL, all dirty pages must be written.
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writepages should _only_ write pages which are present on
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mapping->io_pages.
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->set_page_dirty() is called from various places in the kernel
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when the target page is marked as needing writeback. It may be called
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under spinlock (it cannot block) and is sometimes called with the page
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not locked.
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->bmap() is currently used by legacy ioctl() (FIBMAP) provided by some
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filesystems and by the swapper. The latter will eventually go away. Please,
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keep it that way and don't breed new callers.
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->invalidatepage() is called when the filesystem must attempt to drop
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some or all of the buffers from the page when it is being truncated. It
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returns zero on success. If ->invalidatepage is zero, the kernel uses
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block_invalidatepage() instead.
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->releasepage() is called when the kernel is about to try to drop the
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buffers from the page in preparation for freeing it. It returns zero to
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indicate that the buffers are (or may be) freeable. If ->releasepage is zero,
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the kernel assumes that the fs has no private interest in the buffers.
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->freepage() is called when the kernel is done dropping the page
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from the page cache.
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->launder_page() may be called prior to releasing a page if
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it is still found to be dirty. It returns zero if the page was successfully
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cleaned, or an error value if not. Note that in order to prevent the page
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getting mapped back in and redirtied, it needs to be kept locked
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across the entire operation.
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->swap_activate will be called with a non-zero argument on
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files backing (non block device backed) swapfiles. A return value
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of zero indicates success, in which case this file can be used for
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backing swapspace. The swapspace operations will be proxied to the
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address space operations.
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->swap_deactivate() will be called in the sys_swapoff()
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path after ->swap_activate() returned success.
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----------------------- file_lock_operations ------------------------------
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prototypes:
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void (*fl_copy_lock)(struct file_lock *, struct file_lock *);
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void (*fl_release_private)(struct file_lock *);
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locking rules:
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file_lock_lock may block
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fl_copy_lock: yes no
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fl_release_private: maybe no
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----------------------- lock_manager_operations ---------------------------
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prototypes:
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int (*lm_compare_owner)(struct file_lock *, struct file_lock *);
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void (*lm_notify)(struct file_lock *); /* unblock callback */
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int (*lm_grant)(struct file_lock *, struct file_lock *, int);
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void (*lm_break)(struct file_lock *); /* break_lease callback */
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int (*lm_change)(struct file_lock **, int);
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locking rules:
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file_lock_lock may block
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lm_compare_owner: yes no
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lm_notify: yes no
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lm_grant: no no
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lm_break: yes no
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lm_change yes no
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--------------------------- buffer_head -----------------------------------
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prototypes:
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void (*b_end_io)(struct buffer_head *bh, int uptodate);
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locking rules:
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called from interrupts. In other words, extreme care is needed here.
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bh is locked, but that's all warranties we have here. Currently only RAID1,
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highmem, fs/buffer.c, and fs/ntfs/aops.c are providing these. Block devices
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call this method upon the IO completion.
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--------------------------- block_device_operations -----------------------
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prototypes:
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int (*open) (struct block_device *, fmode_t);
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int (*release) (struct gendisk *, fmode_t);
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int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
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int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
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int (*direct_access) (struct block_device *, sector_t, void **, unsigned long *);
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int (*media_changed) (struct gendisk *);
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void (*unlock_native_capacity) (struct gendisk *);
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int (*revalidate_disk) (struct gendisk *);
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int (*getgeo)(struct block_device *, struct hd_geometry *);
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void (*swap_slot_free_notify) (struct block_device *, unsigned long);
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locking rules:
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bd_mutex
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open: yes
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release: yes
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ioctl: no
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compat_ioctl: no
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direct_access: no
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media_changed: no
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unlock_native_capacity: no
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revalidate_disk: no
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getgeo: no
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swap_slot_free_notify: no (see below)
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media_changed, unlock_native_capacity and revalidate_disk are called only from
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check_disk_change().
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swap_slot_free_notify is called with swap_lock and sometimes the page lock
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held.
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--------------------------- file_operations -------------------------------
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prototypes:
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loff_t (*llseek) (struct file *, loff_t, int);
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ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
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ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
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ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
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ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
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int (*readdir) (struct file *, void *, filldir_t);
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unsigned int (*poll) (struct file *, struct poll_table_struct *);
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long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
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long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
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int (*mmap) (struct file *, struct vm_area_struct *);
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int (*open) (struct inode *, struct file *);
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|
int (*flush) (struct file *);
|
|
int (*release) (struct inode *, struct file *);
|
|
int (*fsync) (struct file *, loff_t start, loff_t end, int datasync);
|
|
int (*aio_fsync) (struct kiocb *, int datasync);
|
|
int (*fasync) (int, struct file *, int);
|
|
int (*lock) (struct file *, int, struct file_lock *);
|
|
ssize_t (*readv) (struct file *, const struct iovec *, unsigned long,
|
|
loff_t *);
|
|
ssize_t (*writev) (struct file *, const struct iovec *, unsigned long,
|
|
loff_t *);
|
|
ssize_t (*sendfile) (struct file *, loff_t *, size_t, read_actor_t,
|
|
void __user *);
|
|
ssize_t (*sendpage) (struct file *, struct page *, int, size_t,
|
|
loff_t *, int);
|
|
unsigned long (*get_unmapped_area)(struct file *, unsigned long,
|
|
unsigned long, unsigned long, unsigned long);
|
|
int (*check_flags)(int);
|
|
int (*flock) (struct file *, int, struct file_lock *);
|
|
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *,
|
|
size_t, unsigned int);
|
|
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *,
|
|
size_t, unsigned int);
|
|
int (*setlease)(struct file *, long, struct file_lock **);
|
|
long (*fallocate)(struct file *, int, loff_t, loff_t);
|
|
};
|
|
|
|
locking rules:
|
|
All may block except for ->setlease.
|
|
No VFS locks held on entry except for ->setlease.
|
|
|
|
->setlease has the file_list_lock held and must not sleep.
|
|
|
|
->llseek() locking has moved from llseek to the individual llseek
|
|
implementations. If your fs is not using generic_file_llseek, you
|
|
need to acquire and release the appropriate locks in your ->llseek().
|
|
For many filesystems, it is probably safe to acquire the inode
|
|
mutex or just to use i_size_read() instead.
|
|
Note: this does not protect the file->f_pos against concurrent modifications
|
|
since this is something the userspace has to take care about.
|
|
|
|
->fasync() is responsible for maintaining the FASYNC bit in filp->f_flags.
|
|
Most instances call fasync_helper(), which does that maintenance, so it's
|
|
not normally something one needs to worry about. Return values > 0 will be
|
|
mapped to zero in the VFS layer.
|
|
|
|
->readdir() and ->ioctl() on directories must be changed. Ideally we would
|
|
move ->readdir() to inode_operations and use a separate method for directory
|
|
->ioctl() or kill the latter completely. One of the problems is that for
|
|
anything that resembles union-mount we won't have a struct file for all
|
|
components. And there are other reasons why the current interface is a mess...
|
|
|
|
->read on directories probably must go away - we should just enforce -EISDIR
|
|
in sys_read() and friends.
|
|
|
|
--------------------------- dquot_operations -------------------------------
|
|
prototypes:
|
|
int (*write_dquot) (struct dquot *);
|
|
int (*acquire_dquot) (struct dquot *);
|
|
int (*release_dquot) (struct dquot *);
|
|
int (*mark_dirty) (struct dquot *);
|
|
int (*write_info) (struct super_block *, int);
|
|
|
|
These operations are intended to be more or less wrapping functions that ensure
|
|
a proper locking wrt the filesystem and call the generic quota operations.
|
|
|
|
What filesystem should expect from the generic quota functions:
|
|
|
|
FS recursion Held locks when called
|
|
write_dquot: yes dqonoff_sem or dqptr_sem
|
|
acquire_dquot: yes dqonoff_sem or dqptr_sem
|
|
release_dquot: yes dqonoff_sem or dqptr_sem
|
|
mark_dirty: no -
|
|
write_info: yes dqonoff_sem
|
|
|
|
FS recursion means calling ->quota_read() and ->quota_write() from superblock
|
|
operations.
|
|
|
|
More details about quota locking can be found in fs/dquot.c.
|
|
|
|
--------------------------- vm_operations_struct -----------------------------
|
|
prototypes:
|
|
void (*open)(struct vm_area_struct*);
|
|
void (*close)(struct vm_area_struct*);
|
|
int (*fault)(struct vm_area_struct*, struct vm_fault *);
|
|
int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
|
|
int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
|
|
|
|
locking rules:
|
|
mmap_sem PageLocked(page)
|
|
open: yes
|
|
close: yes
|
|
fault: yes can return with page locked
|
|
page_mkwrite: yes can return with page locked
|
|
access: yes
|
|
|
|
->fault() is called when a previously not present pte is about
|
|
to be faulted in. The filesystem must find and return the page associated
|
|
with the passed in "pgoff" in the vm_fault structure. If it is possible that
|
|
the page may be truncated and/or invalidated, then the filesystem must lock
|
|
the page, then ensure it is not already truncated (the page lock will block
|
|
subsequent truncate), and then return with VM_FAULT_LOCKED, and the page
|
|
locked. The VM will unlock the page.
|
|
|
|
->page_mkwrite() is called when a previously read-only pte is
|
|
about to become writeable. The filesystem again must ensure that there are
|
|
no truncate/invalidate races, and then return with the page locked. If
|
|
the page has been truncated, the filesystem should not look up a new page
|
|
like the ->fault() handler, but simply return with VM_FAULT_NOPAGE, which
|
|
will cause the VM to retry the fault.
|
|
|
|
->access() is called when get_user_pages() fails in
|
|
acces_process_vm(), typically used to debug a process through
|
|
/proc/pid/mem or ptrace. This function is needed only for
|
|
VM_IO | VM_PFNMAP VMAs.
|
|
|
|
================================================================================
|
|
Dubious stuff
|
|
|
|
(if you break something or notice that it is broken and do not fix it yourself
|
|
- at least put it here)
|