FAILED: patch "[PATCH] autofs: use dentry flags to block walks during expire" failed to apply to 4.4-stable tree

From 7cbdb4a286a60c5d519cb9223fe2134d26870d39 Mon Sep 17 00:00:00 2001

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7cbdb4a286a60c5d519cb9223fe2134d26870d39 Mon Sep 17 00:00:00 2001
From: Ian Kent <[email protected]>
Date: Mon, 19 Sep 2016 14:44:12 -0700
Subject: [PATCH] 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 47be61845c77 ("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 47be61845c77 ("fs/dcache.c: avoid soft-lockup in dput()")

Link:
http://lkml.kernel.org/r/[email protected]

Signed-off-by Ian Kent <[email protected]>

Reported-by Takashi Iwai <[email protected]>

Tested-by Takashi Iwai <[email protected]>

Cc Takashi Iwai <[email protected]>

Cc NeilBrown <[email protected]>

Cc Al Viro <[email protected]>

Cc <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Signed-off-by Linus Torvalds <[email protected]>

fs/autofs4/expire.c +2 -0

index b493909e7492..d8e6d421c27f 100644
@@ -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;
 

fs/autofs4/expire.c +28 -12

 	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)) {
-			if (expired != dentry)
-				dput(dentry);
-			goto found;
-		}
 
+		/* 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);
+
+		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 */

fs/autofs4/expire.c +12 -1

 	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);

On Mon, 2016-09-26 at 09:56 +0200, [email protected] wrote:

Hi Greg,

Quoted 4 lines

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

There is another bug fix from Al Viro upon which this path depends which has not been included in the stable tree.

I recommend that I backport both patches.
Is that acceptable?

Should I include a cover description for the two patches explaining the need for the additional patch or just post the two patches to <[email protected]>?

Quoted 13 lines · Ian Kent

On Mon, 2016-09-26 at 09:56 +0200, [email protected] wrote:

Hi Greg,

Quoted 4 lines

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

There is another bug fix from Al Viro upon which this path depends which has not
been included in the stable tree.

Quoted 2 lines

I recommend that I backport both patches.
Is that acceptable?

Sure, or just give me the git commit id of the patch and I will queue it up as well before I apply this one.

Quoted 5 lines

Should I include a cover description for the two patches explaining the need for
the additional patch or just post the two patches to < [email protected]>?

Well, the correct address would be the good thing to use :)

Other than that, either way is fine.

thanks,

greg k-h