Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull d_inode/d_flags race fix from Al Viro. I love this fix. Not only does it fix the race in the dentry type handling, it entirely gets rid of the nasty and subtle memory ordering rules for d_type and d_inode, and replaces them with the basic dentry locking rules (sequence numbers under RCU, d_lock elsewhere). * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: use ->d_seq to get coherency between ->d_inode and ->d_flags
This commit is contained in:
commit
f691b77b1f
20
fs/dcache.c
20
fs/dcache.c
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@ -269,9 +269,6 @@ static inline int dname_external(const struct dentry *dentry)
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return dentry->d_name.name != dentry->d_iname;
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return dentry->d_name.name != dentry->d_iname;
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}
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}
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/*
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* Make sure other CPUs see the inode attached before the type is set.
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*/
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static inline void __d_set_inode_and_type(struct dentry *dentry,
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static inline void __d_set_inode_and_type(struct dentry *dentry,
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struct inode *inode,
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struct inode *inode,
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unsigned type_flags)
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unsigned type_flags)
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@ -279,28 +276,18 @@ static inline void __d_set_inode_and_type(struct dentry *dentry,
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unsigned flags;
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unsigned flags;
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dentry->d_inode = inode;
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dentry->d_inode = inode;
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smp_wmb();
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flags = READ_ONCE(dentry->d_flags);
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flags = READ_ONCE(dentry->d_flags);
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flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
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flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
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flags |= type_flags;
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flags |= type_flags;
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WRITE_ONCE(dentry->d_flags, flags);
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WRITE_ONCE(dentry->d_flags, flags);
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}
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}
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/*
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* Ideally, we want to make sure that other CPUs see the flags cleared before
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* the inode is detached, but this is really a violation of RCU principles
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* since the ordering suggests we should always set inode before flags.
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*
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* We should instead replace or discard the entire dentry - but that sucks
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* performancewise on mass deletion/rename.
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*/
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static inline void __d_clear_type_and_inode(struct dentry *dentry)
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static inline void __d_clear_type_and_inode(struct dentry *dentry)
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{
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{
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unsigned flags = READ_ONCE(dentry->d_flags);
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unsigned flags = READ_ONCE(dentry->d_flags);
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flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
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flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
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WRITE_ONCE(dentry->d_flags, flags);
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WRITE_ONCE(dentry->d_flags, flags);
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smp_wmb();
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dentry->d_inode = NULL;
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dentry->d_inode = NULL;
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}
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}
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@ -370,9 +357,11 @@ static void dentry_unlink_inode(struct dentry * dentry)
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__releases(dentry->d_inode->i_lock)
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__releases(dentry->d_inode->i_lock)
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{
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{
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struct inode *inode = dentry->d_inode;
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struct inode *inode = dentry->d_inode;
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raw_write_seqcount_begin(&dentry->d_seq);
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__d_clear_type_and_inode(dentry);
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__d_clear_type_and_inode(dentry);
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hlist_del_init(&dentry->d_u.d_alias);
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hlist_del_init(&dentry->d_u.d_alias);
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dentry_rcuwalk_invalidate(dentry);
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raw_write_seqcount_end(&dentry->d_seq);
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spin_unlock(&dentry->d_lock);
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spin_unlock(&dentry->d_lock);
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spin_unlock(&inode->i_lock);
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spin_unlock(&inode->i_lock);
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if (!inode->i_nlink)
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if (!inode->i_nlink)
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@ -1758,8 +1747,9 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
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spin_lock(&dentry->d_lock);
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spin_lock(&dentry->d_lock);
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if (inode)
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if (inode)
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hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
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hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
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raw_write_seqcount_begin(&dentry->d_seq);
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__d_set_inode_and_type(dentry, inode, add_flags);
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__d_set_inode_and_type(dentry, inode, add_flags);
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dentry_rcuwalk_invalidate(dentry);
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raw_write_seqcount_end(&dentry->d_seq);
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spin_unlock(&dentry->d_lock);
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spin_unlock(&dentry->d_lock);
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fsnotify_d_instantiate(dentry, inode);
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fsnotify_d_instantiate(dentry, inode);
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}
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}
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@ -409,9 +409,7 @@ static inline bool d_mountpoint(const struct dentry *dentry)
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*/
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*/
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static inline unsigned __d_entry_type(const struct dentry *dentry)
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static inline unsigned __d_entry_type(const struct dentry *dentry)
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{
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{
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unsigned type = READ_ONCE(dentry->d_flags);
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return dentry->d_flags & DCACHE_ENTRY_TYPE;
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smp_rmb();
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return type & DCACHE_ENTRY_TYPE;
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}
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}
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static inline bool d_is_miss(const struct dentry *dentry)
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static inline bool d_is_miss(const struct dentry *dentry)
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