Commit 7cbdb4a2 authored by Ian Kent's avatar Ian Kent Committed by Linus Torvalds
Browse files

autofs: use dentry flags to block walks during expire 

Somewhere along the way the autofs expire operation has changed to hold
a spin lock over expired dentry selection.  The autofs indirect mount
expired dentry selection is complicated and quite lengthy so it isn't
appropriate to hold a spin lock over the operation.

Commit 47be6184 ("fs/dcache.c: avoid soft-lockup in dput()") added a
might_sleep() to dput() causing a WARN_ONCE() about this usage to be
issued.

But the spin lock doesn't need to be held over this check, the autofs
dentry info.  flags are enough to block walks into dentrys during the
expire.

I've left the direct mount expire as it is (for now) because it is much
simpler and quicker than the indirect mount expire and adding spin lock
release and re-aquires would do nothing more than add overhead.

Fixes: 47be6184 ("fs/dcache.c: avoid soft-lockup in dput()")
Link: http://lkml.kernel.org/r/20160912014017.1773.73060.stgit@pluto.themaw.net


Signed-off-by: default avatarIan Kent <raven@themaw.net>
Reported-by: default avatarTakashi Iwai <tiwai@suse.de>
Tested-by: default avatarTakashi Iwai <tiwai@suse.de>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: NeilBrown <neilb@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 08eeb306

fs/autofs4/expire.c

+42 −13
Original line number Diff line number Diff line
@@ -417,6 +417,7 @@ static struct dentry *should_expire(struct dentry *dentry, 
	}

	return NULL;

}



/*

 * Find an eligible tree to time-out

 * A tree is eligible if :-
@@ -432,6 +433,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 
	struct dentry *root = sb->s_root;

	struct dentry *dentry;

	struct dentry *expired;

	struct dentry *found;

	struct autofs_info *ino;



	if (!root)
@@ -442,31 +444,46 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 


	dentry = NULL;

	while ((dentry = get_next_positive_subdir(dentry, root))) {

		int flags = how;



		spin_lock(&sbi->fs_lock);

		ino = autofs4_dentry_ino(dentry);

		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)

			expired = NULL;

		else

			expired = should_expire(dentry, mnt, timeout, how);

		if (!expired) {

		if (ino->flags & AUTOFS_INF_WANT_EXPIRE) {

			spin_unlock(&sbi->fs_lock);

			continue;

		}

		spin_unlock(&sbi->fs_lock);



		expired = should_expire(dentry, mnt, timeout, flags);

		if (!expired)

			continue;



		spin_lock(&sbi->fs_lock);

		ino = autofs4_dentry_ino(expired);

		ino->flags |= AUTOFS_INF_WANT_EXPIRE;

		spin_unlock(&sbi->fs_lock);

		synchronize_rcu();

		spin_lock(&sbi->fs_lock);

		if (should_expire(expired, mnt, timeout, how)) {



		/* Make sure a reference is not taken on found if

		 * things have changed.

		 */

		flags &= ~AUTOFS_EXP_LEAVES;

		found = should_expire(expired, mnt, timeout, how);

		if (!found || found != expired)

			/* Something has changed, continue */

			goto next;



		if (expired != dentry)

			dput(dentry);

			goto found;

		}



		spin_lock(&sbi->fs_lock);

		goto found;

next:

		spin_lock(&sbi->fs_lock);

		ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;

		spin_unlock(&sbi->fs_lock);

		if (expired != dentry)

			dput(expired);

		spin_unlock(&sbi->fs_lock);

	}

	return NULL;
@@ -483,6 +500,7 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) 
	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);

	struct autofs_info *ino = autofs4_dentry_ino(dentry);

	int status;

	int state;



	/* Block on any pending expire */

	if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE))
@@ -490,8 +508,19 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) 
	if (rcu_walk)

		return -ECHILD;



retry:

	spin_lock(&sbi->fs_lock);

	if (ino->flags & AUTOFS_INF_EXPIRING) {

	state = ino->flags & (AUTOFS_INF_WANT_EXPIRE | AUTOFS_INF_EXPIRING);

	if (state == AUTOFS_INF_WANT_EXPIRE) {

		spin_unlock(&sbi->fs_lock);

		/*

		 * Possibly being selected for expire, wait until

		 * it's selected or not.

		 */

		schedule_timeout_uninterruptible(HZ/10);

		goto retry;

	}

	if (state & AUTOFS_INF_EXPIRING) {

		spin_unlock(&sbi->fs_lock);



		pr_debug("waiting for expire %p name=%pd\n", dentry, dentry);

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