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autofs4: fix direct mount pending expire race

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For direct and offset type mounts that are covered by another mount we
cannot check the AUTOFS_INF_EXPIRING flag during a path walk which leads
to lookups walking into an expiring mount while it is being expired.

For example, for the direct multi-mount map entry with a couple of
offsets:

/race/mm1  /      <server1>:/<path1>
           /om1   <server2>:/<path2>
           /om2   <server1>:/<path3>

an autofs trigger mount is mounted on /race/mm1 and when accessed it is
over mounted and trigger mounts made for /race/mm1/om1 and /race/mm1/om2.
So it isn't possible for path walks to see the expiring flag at all and
they happily walk into the file system while it is expiring.

When expiring these mounts follow_down() must stop at the autofs mount and
all processes must block in the ->follow_link() method (except the daemon)
until the expire is complete.  This is done by decrementing the d_mounted
field of the autofs trigger mount root dentry until the expire is
completed.  In ->follow_link() all processes wait on the expire and the
mount following is completed for the daemon until the expire is complete.

Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ian Kent 2008-07-23 21:30:27 -07:00 committed by Linus Torvalds
parent 97e7449a7a
commit 6e60a9ab5f
3 changed files with 65 additions and 26 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

3
fs/autofs4/autofs_i.h
View file

@ -52,6 +52,8 @@ struct autofs_info {
int flags;
struct completion expire_complete;
struct list_head active;
struct list_head expiring;
@ -69,6 +71,7 @@ struct autofs_info {
};
#define AUTOFS_INF_EXPIRING (1<<0) /* dentry is in the process of expiring */
#define AUTOFS_INF_MOUNTPOINT (1<<1) /* mountpoint status for direct expire */
struct autofs_wait_queue {
wait_queue_head_t queue;

16
fs/autofs4/expire.c
View file

@ -259,13 +259,15 @@ static struct dentry *autofs4_expire_direct(struct super_block *sb,
now = jiffies;
timeout = sbi->exp_timeout;
/* Lock the tree as we must expire as a whole */
spin_lock(&sbi->fs_lock);
if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
struct autofs_info *ino = autofs4_dentry_ino(root);
/* Set this flag early to catch sys_chdir and the like */
if (d_mountpoint(root)) {
ino->flags |= AUTOFS_INF_MOUNTPOINT;
root->d_mounted--;
}
ino->flags |= AUTOFS_INF_EXPIRING;
init_completion(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
return root;
}
@ -392,6 +394,7 @@ found:
expired, (int)expired->d_name.len, expired->d_name.name);
ino = autofs4_dentry_ino(expired);
ino->flags |= AUTOFS_INF_EXPIRING;
init_completion(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
spin_lock(&dcache_lock);
list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
@ -429,6 +432,7 @@ int autofs4_expire_run(struct super_block *sb,
spin_lock(&sbi->fs_lock);
ino = autofs4_dentry_ino(dentry);
ino->flags &= ~AUTOFS_INF_EXPIRING;
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
return ret;
@ -457,8 +461,14 @@ int autofs4_expire_multi(struct super_block *sb, struct vfsmount *mnt,
/* This is synchronous because it makes the daemon a
little easier */
ret = autofs4_wait(sbi, dentry, NFY_EXPIRE);
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_MOUNTPOINT) {
sb->s_root->d_mounted++;
ino->flags &= ~AUTOFS_INF_MOUNTPOINT;
}
ino->flags &= ~AUTOFS_INF_EXPIRING;
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);
dput(dentry);
}

72
fs/autofs4/root.c
View file

@ -141,6 +141,7 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
dentry, dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_NONE);
wait_for_completion(&ino->expire_complete);
DPRINTK("expire done status=%d", status);
@ -227,14 +228,32 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d",
dentry, dentry->d_name.len, dentry->d_name.name, oz_mode,
nd->flags);
/* If it's our master or we shouldn't trigger a mount we're done */
lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS);
if (oz_mode ||
!(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING))
/*
* For an expire of a covered direct or offset mount we need
* to beeak out of follow_down() at the autofs mount trigger
* (d_mounted--), so we can see the expiring flag, and manage
* the blocking and following here until the expire is completed.
*/
if (oz_mode) {
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_EXPIRING) {
spin_unlock(&sbi->fs_lock);
/* Follow down to our covering mount. */
if (!follow_down(&nd->path.mnt, &nd->path.dentry))
goto done;
/*
* We shouldn't need to do this but we have no way
* of knowing what may have been done so try a follow
* just in case.
*/
autofs4_follow_mount(&nd->path.mnt, &nd->path.dentry);
goto done;
}
spin_unlock(&sbi->fs_lock);
goto done;
}
/* If an expire request is pending wait for it. */
/* If an expire request is pending everyone must wait. */
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_EXPIRING) {
spin_unlock(&sbi->fs_lock);
@ -243,6 +262,7 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
dentry, dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_NONE);
wait_for_completion(&ino->expire_complete);
DPRINTK("request done status=%d", status);
@ -250,10 +270,15 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
}
spin_unlock(&sbi->fs_lock);
cont:
/* We trigger a mount for almost all flags */
lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS);
if (!(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING))
goto done;
/*
* If the dentry contains directories then it is an
* autofs multi-mount with no root mount offset. So
* don't try to mount it again.
* If the dentry contains directories then it is an autofs
* multi-mount with no root mount offset. So don't try to
* mount it again.
*/
spin_lock(&dcache_lock);
if (dentry->d_flags & DCACHE_AUTOFS_PENDING ||
@ -264,22 +289,22 @@ cont:
if (status)
goto out_error;
/*
* The mount succeeded but if there is no root mount
* it must be an autofs multi-mount with no root offset
* so we don't need to follow the mount.
*/
if (d_mountpoint(dentry)) {
if (!autofs4_follow_mount(&nd->path.mnt,
&nd->path.dentry)) {
status = -ENOENT;
goto out_error;
}
}
goto done;
goto follow;
}
spin_unlock(&dcache_lock);
follow:
/*
* If there is no root mount it must be an autofs
* multi-mount with no root offset so we don't need
* to follow it.
*/
if (d_mountpoint(dentry)) {
if (!autofs4_follow_mount(&nd->path.mnt,
&nd->path.dentry)) {
status = -ENOENT;
goto out_error;
}
}
done:
return NULL;
@ -545,6 +570,7 @@ static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, s
expiring, expiring->d_name.len,
expiring->d_name.name);
autofs4_wait(sbi, expiring, NFY_NONE);
wait_for_completion(&ino->expire_complete);
DPRINTK("request completed");
goto cont;
}