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autofs4: fix indirect mount pending expire race

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The selection of a dentry for expiration and the setting of the
AUTOFS_INF_EXPIRING flag isn't done atomically which can lead to lookups
walking into an expiring mount.

What happens is that an expire is initiated by the daemon and a dentry is
selected for expire but, since there is no lock held between the selection
and setting of the expiring flag, a process may find the flag clear and
continue walking into the mount tree at the same time the daemon attempts
the expire it.

Signed-off-by: Ian Kent <raven@themaw.net>
Reviewed-by: 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 21:30:26 -07:00
committed by Linus Torvalds
parent 26e81b3142
commit 97e7449a7a
3 changed files with 65 additions and 23 deletions
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32
fs/autofs4/root.c
View File

@ -133,7 +133,10 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
/* Block on any pending expiry here; invalidate the dentry
when expiration is done to trigger mount request with a new
dentry */
if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_EXPIRING) {
spin_unlock(&sbi->fs_lock);
DPRINTK("waiting for expire %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
@ -149,8 +152,11 @@ static int try_to_fill_dentry(struct dentry *dentry, int flags)
status = d_invalidate(dentry);
if (status != -EBUSY)
return -EAGAIN;
}
goto cont;
}
spin_unlock(&sbi->fs_lock);
cont:
DPRINTK("dentry=%p %.*s ino=%p",
dentry, dentry->d_name.len, dentry->d_name.name, dentry->d_inode);
@ -229,15 +235,21 @@ static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
goto done;
/* If an expire request is pending wait for it. */
if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_EXPIRING) {
spin_unlock(&sbi->fs_lock);
DPRINTK("waiting for active request %p name=%.*s",
dentry, dentry->d_name.len, dentry->d_name.name);
status = autofs4_wait(sbi, dentry, NFY_NONE);
DPRINTK("request done status=%d", status);
}
goto cont;
}
spin_unlock(&sbi->fs_lock);
cont:
/*
* If the dentry contains directories then it is an
* autofs multi-mount with no root mount offset. So
@ -292,8 +304,11 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
int status = 1;
/* Pending dentry */
spin_lock(&sbi->fs_lock);
if (autofs4_ispending(dentry)) {
/* The daemon never causes a mount to trigger */
spin_unlock(&sbi->fs_lock);
if (oz_mode)
return 1;
@ -316,6 +331,7 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
return status;
}
spin_unlock(&sbi->fs_lock);
/* Negative dentry.. invalidate if "old" */
if (dentry->d_inode == NULL)
@ -329,6 +345,7 @@ static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
DPRINTK("dentry=%p %.*s, emptydir",
dentry, dentry->d_name.len, dentry->d_name.name);
spin_unlock(&dcache_lock);
/* The daemon never causes a mount to trigger */
if (oz_mode)
return 1;
@ -521,13 +538,18 @@ static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, s
* so it must have been successful, so just wait for it.
*/
ino = autofs4_dentry_ino(expiring);
while (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
spin_lock(&sbi->fs_lock);
if (ino->flags & AUTOFS_INF_EXPIRING) {
spin_unlock(&sbi->fs_lock);
DPRINTK("wait for incomplete expire %p name=%.*s",
expiring, expiring->d_name.len,
expiring->d_name.name);
autofs4_wait(sbi, expiring, NFY_NONE);
DPRINTK("request completed");
goto cont;
}
spin_unlock(&sbi->fs_lock);
cont:
spin_lock(&sbi->lookup_lock);
if (!list_empty(&ino->expiring))
list_del_init(&ino->expiring);