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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
Download Patch File Download Diff File Expand all files Collapse all files

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);
}