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remarkable-linux/fs/autofs4/inode.c
Ian Kent 2576737873 autofs4: use look aside list for lookups 
A while ago a patch to resolve a deadlock during directory creation was
merged.  This delayed the hashing of lookup dentrys until the ->mkdir()
(or ->symlink()) operation completed to ensure we always went through
->lookup() instead of also having processes go through ->revalidate() so
our VFS locking remained consistent.

Now we are seeing a couple of side affects of that change in situations
with heavy mount activity.

Two cases have been identified:

1) When a mount request is triggered, due to the delayed hashing, the
   directory created by user space for the mount point doesn't have the
   DCACHE_AUTOFS_PENDING flag set.  In the case of an autofs multi-mount
   where a tree of mount point directories are created this can lead to
   the path walk continuing rather than the dentry being sent to the wait
   queue to wait for request completion.  This is because, if the pending
   flag isn't set, the criteria for deciding this is a mount in progress
   fails to hold, namely that the dentry is not a mount point and has no
   subdirectories.

2) A mount request dentry is initially created negative and unhashed.
   It remains this way until the ->mkdir() callback completes.  Since it
   is unhashed a fresh dentry is used when the user space mount request
   creates the mount point directory.  This leaves the original dentry
   negative and unhashed.  But revalidate has no way to tell the VFS that
   the dentry has changed, other than to force another ->lookup() by
   returning false, which is at best wastefull and at worst not possible.
   This results in an -ENOENT return from the original path walk when in
   fact the mount succeeded.

To resolve this we need to ensure that the same dentry is used in all
calls to ->lookup() during the course of a mount request.  This patch
achieves that by adding the initial dentry to a look aside list and
removes it at ->mkdir() or ->symlink() completion (or when the dentry is
released), since these are the only create operations autofs4 supports.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-24 10:47:31 -07:00

474 lines
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/* -*- c -*- --------------------------------------------------------------- *
*
* linux/fs/autofs/inode.c
*
* Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
* Copyright 2005-2006 Ian Kent <raven@themaw.net>
*
* This file is part of the Linux kernel and is made available under
* the terms of the GNU General Public License, version 2, or at your
* option, any later version, incorporated herein by reference.
*
* ------------------------------------------------------------------------- */
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/seq_file.h>
#include <linux/pagemap.h>
#include <linux/parser.h>
#include <linux/bitops.h>
#include <linux/magic.h>
#include "autofs_i.h"
#include <linux/module.h>
static void ino_lnkfree(struct autofs_info *ino)
{
if (ino->u.symlink) {
kfree(ino->u.symlink);
ino->u.symlink = NULL;
}
}
struct autofs_info *autofs4_init_ino(struct autofs_info *ino,
struct autofs_sb_info *sbi, mode_t mode)
{
int reinit = 1;
if (ino == NULL) {
reinit = 0;
ino = kmalloc(sizeof(*ino), GFP_KERNEL);
}
if (ino == NULL)
return NULL;
if (!reinit) {
ino->flags = 0;
ino->inode = NULL;
ino->dentry = NULL;
ino->size = 0;
INIT_LIST_HEAD(&ino->active);
INIT_LIST_HEAD(&ino->expiring);
atomic_set(&ino->count, 0);
}
ino->mode = mode;
ino->last_used = jiffies;
ino->sbi = sbi;
if (reinit && ino->free)
(ino->free)(ino);
memset(&ino->u, 0, sizeof(ino->u));
ino->free = NULL;
if (S_ISLNK(mode))
ino->free = ino_lnkfree;
return ino;
}
void autofs4_free_ino(struct autofs_info *ino)
{
struct autofs_info *p_ino;
if (ino->dentry) {
ino->dentry->d_fsdata = NULL;
if (ino->dentry->d_inode) {
struct dentry *parent = ino->dentry->d_parent;
if (atomic_dec_and_test(&ino->count)) {
p_ino = autofs4_dentry_ino(parent);
if (p_ino && parent != ino->dentry)
atomic_dec(&p_ino->count);
}
dput(ino->dentry);
}
ino->dentry = NULL;
}
if (ino->free)
(ino->free)(ino);
kfree(ino);
}
/*
* Deal with the infamous "Busy inodes after umount ..." message.
*
* Clean up the dentry tree. This happens with autofs if the user
* space program goes away due to a SIGKILL, SIGSEGV etc.
*/
static void autofs4_force_release(struct autofs_sb_info *sbi)
{
struct dentry *this_parent = sbi->sb->s_root;
struct list_head *next;
if (!sbi->sb->s_root)
return;
spin_lock(&dcache_lock);
repeat:
next = this_parent->d_subdirs.next;
resume:
while (next != &this_parent->d_subdirs) {
struct dentry *dentry = list_entry(next, struct dentry, d_u.d_child);
/* Negative dentry - don`t care */
if (!simple_positive(dentry)) {
next = next->next;
continue;
}
if (!list_empty(&dentry->d_subdirs)) {
this_parent = dentry;
goto repeat;
}
next = next->next;
spin_unlock(&dcache_lock);
DPRINTK("dentry %p %.*s",
dentry, (int)dentry->d_name.len, dentry->d_name.name);
dput(dentry);
spin_lock(&dcache_lock);
}
if (this_parent != sbi->sb->s_root) {
struct dentry *dentry = this_parent;
next = this_parent->d_u.d_child.next;
this_parent = this_parent->d_parent;
spin_unlock(&dcache_lock);
DPRINTK("parent dentry %p %.*s",
dentry, (int)dentry->d_name.len, dentry->d_name.name);
dput(dentry);
spin_lock(&dcache_lock);
goto resume;
}
spin_unlock(&dcache_lock);
}
void autofs4_kill_sb(struct super_block *sb)
{
struct autofs_sb_info *sbi = autofs4_sbi(sb);
/*
* In the event of a failure in get_sb_nodev the superblock
* info is not present so nothing else has been setup, so
* just call kill_anon_super when we are called from
* deactivate_super.
*/
if (!sbi)
goto out_kill_sb;
if (!sbi->catatonic)
autofs4_catatonic_mode(sbi); /* Free wait queues, close pipe */
/* Clean up and release dangling references */
autofs4_force_release(sbi);
sb->s_fs_info = NULL;
kfree(sbi);
out_kill_sb:
DPRINTK("shutting down");
kill_anon_super(sb);
}
static int autofs4_show_options(struct seq_file *m, struct vfsmount *mnt)
{
struct autofs_sb_info *sbi = autofs4_sbi(mnt->mnt_sb);
struct inode *root_inode = mnt->mnt_sb->s_root->d_inode;
if (!sbi)
return 0;
seq_printf(m, ",fd=%d", sbi->pipefd);
if (root_inode->i_uid != 0)
seq_printf(m, ",uid=%u", root_inode->i_uid);
if (root_inode->i_gid != 0)
seq_printf(m, ",gid=%u", root_inode->i_gid);
seq_printf(m, ",pgrp=%d", sbi->oz_pgrp);
seq_printf(m, ",timeout=%lu", sbi->exp_timeout/HZ);
seq_printf(m, ",minproto=%d", sbi->min_proto);
seq_printf(m, ",maxproto=%d", sbi->max_proto);
if (sbi->type & AUTOFS_TYPE_OFFSET)
seq_printf(m, ",offset");
else if (sbi->type & AUTOFS_TYPE_DIRECT)
seq_printf(m, ",direct");
else
seq_printf(m, ",indirect");
return 0;
}
static const struct super_operations autofs4_sops = {
.statfs = simple_statfs,
.show_options = autofs4_show_options,
};
enum {Opt_err, Opt_fd, Opt_uid, Opt_gid, Opt_pgrp, Opt_minproto, Opt_maxproto,
Opt_indirect, Opt_direct, Opt_offset};
static match_table_t tokens = {
{Opt_fd, "fd=%u"},
{Opt_uid, "uid=%u"},
{Opt_gid, "gid=%u"},
{Opt_pgrp, "pgrp=%u"},
{Opt_minproto, "minproto=%u"},
{Opt_maxproto, "maxproto=%u"},
{Opt_indirect, "indirect"},
{Opt_direct, "direct"},
{Opt_offset, "offset"},
{Opt_err, NULL}
};
static int parse_options(char *options, int *pipefd, uid_t *uid, gid_t *gid,
pid_t *pgrp, unsigned int *type, int *minproto, int *maxproto)
{
char *p;
substring_t args[MAX_OPT_ARGS];
int option;
*uid = current->uid;
*gid = current->gid;
*pgrp = task_pgrp_nr(current);
*minproto = AUTOFS_MIN_PROTO_VERSION;
*maxproto = AUTOFS_MAX_PROTO_VERSION;
*pipefd = -1;
if (!options)
return 1;
while ((p = strsep(&options, ",")) != NULL) {
int token;
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_fd:
if (match_int(args, pipefd))
return 1;
break;
case Opt_uid:
if (match_int(args, &option))
return 1;
*uid = option;
break;
case Opt_gid:
if (match_int(args, &option))
return 1;
*gid = option;
break;
case Opt_pgrp:
if (match_int(args, &option))
return 1;
*pgrp = option;
break;
case Opt_minproto:
if (match_int(args, &option))
return 1;
*minproto = option;
break;
case Opt_maxproto:
if (match_int(args, &option))
return 1;
*maxproto = option;
break;
case Opt_indirect:
*type = AUTOFS_TYPE_INDIRECT;
break;
case Opt_direct:
*type = AUTOFS_TYPE_DIRECT;
break;
case Opt_offset:
*type = AUTOFS_TYPE_DIRECT | AUTOFS_TYPE_OFFSET;
break;
default:
return 1;
}
}
return (*pipefd < 0);
}
static struct autofs_info *autofs4_mkroot(struct autofs_sb_info *sbi)
{
struct autofs_info *ino;
ino = autofs4_init_ino(NULL, sbi, S_IFDIR | 0755);
if (!ino)
return NULL;
return ino;
}
static struct dentry_operations autofs4_sb_dentry_operations = {
.d_release = autofs4_dentry_release,
};
int autofs4_fill_super(struct super_block *s, void *data, int silent)
{
struct inode * root_inode;
struct dentry * root;
struct file * pipe;
int pipefd;
struct autofs_sb_info *sbi;
struct autofs_info *ino;
sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
if (!sbi)
goto fail_unlock;
DPRINTK("starting up, sbi = %p",sbi);
s->s_fs_info = sbi;
sbi->magic = AUTOFS_SBI_MAGIC;
sbi->pipefd = -1;
sbi->pipe = NULL;
sbi->catatonic = 1;
sbi->exp_timeout = 0;
sbi->oz_pgrp = task_pgrp_nr(current);
sbi->sb = s;
sbi->version = 0;
sbi->sub_version = 0;
sbi->type = 0;
sbi->min_proto = 0;
sbi->max_proto = 0;
mutex_init(&sbi->wq_mutex);
spin_lock_init(&sbi->fs_lock);
sbi->queues = NULL;
spin_lock_init(&sbi->lookup_lock);
INIT_LIST_HEAD(&sbi->active_list);
INIT_LIST_HEAD(&sbi->expiring_list);
s->s_blocksize = 1024;
s->s_blocksize_bits = 10;
s->s_magic = AUTOFS_SUPER_MAGIC;
s->s_op = &autofs4_sops;
s->s_time_gran = 1;
/*
* Get the root inode and dentry, but defer checking for errors.
*/
ino = autofs4_mkroot(sbi);
if (!ino)
goto fail_free;
root_inode = autofs4_get_inode(s, ino);
if (!root_inode)
goto fail_ino;
root = d_alloc_root(root_inode);
if (!root)
goto fail_iput;
pipe = NULL;
root->d_op = &autofs4_sb_dentry_operations;
root->d_fsdata = ino;
/* Can this call block? */
if (parse_options(data, &pipefd, &root_inode->i_uid, &root_inode->i_gid,
&sbi->oz_pgrp, &sbi->type, &sbi->min_proto,
&sbi->max_proto)) {
printk("autofs: called with bogus options\n");
goto fail_dput;
}
root_inode->i_fop = &autofs4_root_operations;
root_inode->i_op = sbi->type & AUTOFS_TYPE_DIRECT ?
&autofs4_direct_root_inode_operations :
&autofs4_indirect_root_inode_operations;
/* Couldn't this be tested earlier? */
if (sbi->max_proto < AUTOFS_MIN_PROTO_VERSION ||
sbi->min_proto > AUTOFS_MAX_PROTO_VERSION) {
printk("autofs: kernel does not match daemon version "
"daemon (%d, %d) kernel (%d, %d)\n",
sbi->min_proto, sbi->max_proto,
AUTOFS_MIN_PROTO_VERSION, AUTOFS_MAX_PROTO_VERSION);
goto fail_dput;
}
/* Establish highest kernel protocol version */
if (sbi->max_proto > AUTOFS_MAX_PROTO_VERSION)
sbi->version = AUTOFS_MAX_PROTO_VERSION;
else
sbi->version = sbi->max_proto;
sbi->sub_version = AUTOFS_PROTO_SUBVERSION;
DPRINTK("pipe fd = %d, pgrp = %u", pipefd, sbi->oz_pgrp);
pipe = fget(pipefd);
if (!pipe) {
printk("autofs: could not open pipe file descriptor\n");
goto fail_dput;
}
if (!pipe->f_op || !pipe->f_op->write)
goto fail_fput;
sbi->pipe = pipe;
sbi->pipefd = pipefd;
sbi->catatonic = 0;
/*
* Success! Install the root dentry now to indicate completion.
*/
s->s_root = root;
return 0;
/*
* Failure ... clean up.
*/
fail_fput:
printk("autofs: pipe file descriptor does not contain proper ops\n");
fput(pipe);
/* fall through */
fail_dput:
dput(root);
goto fail_free;
fail_iput:
printk("autofs: get root dentry failed\n");
iput(root_inode);
fail_ino:
kfree(ino);
fail_free:
kfree(sbi);
s->s_fs_info = NULL;
fail_unlock:
return -EINVAL;
}
struct inode *autofs4_get_inode(struct super_block *sb,
struct autofs_info *inf)
{
struct inode *inode = new_inode(sb);
if (inode == NULL)
return NULL;
inf->inode = inode;
inode->i_mode = inf->mode;
if (sb->s_root) {
inode->i_uid = sb->s_root->d_inode->i_uid;
inode->i_gid = sb->s_root->d_inode->i_gid;
} else {
inode->i_uid = 0;
inode->i_gid = 0;
}
inode->i_blocks = 0;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
if (S_ISDIR(inf->mode)) {
inode->i_nlink = 2;
inode->i_op = &autofs4_dir_inode_operations;
inode->i_fop = &autofs4_dir_operations;
} else if (S_ISLNK(inf->mode)) {
inode->i_size = inf->size;
inode->i_op = &autofs4_symlink_inode_operations;
}
return inode;
}
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