FAILED: patch "[PATCH] nfsd: fix delegation_blocked() to block correctly for at" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-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]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 45bb63ed20e02ae146336412889fe5450316a84f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024100728-graves-septic-4380@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

45bb63ed20e0 ("nfsd: fix delegation_blocked() to block correctly for at least 30 seconds") b3f255ef6bff ("nfsd: use ktime_get_seconds() for timestamps")

thanks,

greg k-h

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

From 45bb63ed20e02ae146336412889fe5450316a84f Mon Sep 17 00:00:00 2001
From: NeilBrown <[email protected]>
Date: Mon, 9 Sep 2024 15:06:36 +1000
Subject: [PATCH] nfsd: fix delegation_blocked() to block correctly for at
least 30 seconds

The pair of bloom filtered used by delegation_blocked() was intended to block delegations on given filehandles for between 30 and 60 seconds. A new filehandle would be recorded in the "new" bit set. That would then be switch to the "old" bit set between 0 and 30 seconds later, and it would remain as the "old" bit set for 30 seconds.

Unfortunately the code intended to clear the old bit set once it reached 30 seconds old, preparing it to be the next new bit set, instead cleared the *new* bit set before switching it to be the old bit set. This means that the "old" bit set is always empty and delegations are blocked between 0 and 30 seconds.

This patch updates bd->new before clearing the set with that index, instead of afterwards.

index cb5a9ab451c5..ac1859c7cc9d 100644
@@ -1078,7 +1078,8 @@ static void nfs4_free_deleg(struct nfs4_stid *stid)
  * When a delegation is recalled, the filehandle is stored in the "new"
  * filter.
  * Every 30 seconds we swap the filters and clear the "new" one,
- * unless both are empty of course.
+ * unless both are empty of course.  This results in delegations for a
+ * given filehandle being blocked for between 30 and 60 seconds.
  *
  * Each filter is 256 bits.  We hash the filehandle to 32bit and use the
  * low 3 bytes as hash-table indices.

@@ -1107,9 +1108,9 @@ static int delegation_blocked(struct knfsd_fh *fh)
 		if (ktime_get_seconds() - bd->swap_time > 30) {
 			bd->entries -= bd->old_entries;
 			bd->old_entries = bd->entries;
+			bd->new = 1-bd->new;
 			memset(bd->set[bd->new], 0,
 			       sizeof(bd->set[0]));
-			bd->new = 1-bd->new;
 			bd->swap_time = ktime_get_seconds();
 		}
 		spin_unlock(&blocked_delegations_lock);

The pair of bloom filtered used by delegation_blocked() was intended to block delegations on given filehandles for between 30 and 60 seconds. A new filehandle would be recorded in the "new" bit set. That would then be switch to the "old" bit set between 0 and 30 seconds later, and it would remain as the "old" bit set for 30 seconds.

Unfortunately the code intended to clear the old bit set once it reached 30 seconds old, preparing it to be the next new bit set, instead cleared the *new* bit set before switching it to be the old bit set. This means that the "old" bit set is always empty and delegations are blocked between 0 and 30 seconds.

This patch updates bd->new before clearing the set with that index, instead of afterwards.

---
 fs/nfsd/nfs4state.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

index a0aa7e63739d..378639f04a7b 100644
@@ -820,7 +820,8 @@ static void nfs4_free_deleg(struct nfs4_stid *stid)
  * When a delegation is recalled, the filehandle is stored in the "new"
  * filter.
  * Every 30 seconds we swap the filters and clear the "new" one,
- * unless both are empty of course.
+ * unless both are empty of course.  This results in delegations for a
+ * given filehandle being blocked for between 30 and 60 seconds.
  *
  * Each filter is 256 bits.  We hash the filehandle to 32bit and use the
  * low 3 bytes as hash-table indices.

@@ -849,9 +850,9 @@ static int delegation_blocked(struct knfsd_fh *fh)
 		if (seconds_since_boot() - bd->swap_time > 30) {
 			bd->entries -= bd->old_entries;
 			bd->old_entries = bd->entries;
+			bd->new = 1-bd->new;
 			memset(bd->set[bd->new], 0,
 			       sizeof(bd->set[0]));
-			bd->new = 1-bd->new;
 			bd->swap_time = seconds_since_boot();
 		}
 		spin_unlock(&blocked_delegations_lock);

base-commit: 661f109c057497c8baf507a2562ceb9f9fb3cbc2

2.46.0