FAILED: patch "[PATCH] NFSD: Send a meaningful CB_RECALL_ANY keep count" failed to apply to 5.10-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.10-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 <stable@vger.kernel.org>.

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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 9af39c0773ef956039e1ebe9c235532fe6ee1e50
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026110419-postwar-grunge-8e90@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From 9af39c0773ef956039e1ebe9c235532fe6ee1e50 Mon Sep 17 00:00:00 2001
From: Chuck Lever <cel@kernel.org>
Date: Mon, 17 Aug 2026 21:08:39 -0400
Subject: [PATCH] NFSD: Send a meaningful CB_RECALL_ANY keep count

deleg_reaper() sets craa_objects_to_keep to zero on every
CB_RECALL_ANY. RFC 8881 Section 20.6.3 defines that field as the
number of objects the client may keep, leaving the client to choose
which of the excess to return, because the server cannot read lack
of recent use as lack of usefulness. Zero asks for every delegation
the client holds, including the ones backing files an application
still has open.

There is also no reason NFSD has to reclaim the entire delegation
working set on the first sign of memory pressure.

Derive the keep count from cl_deleg_count so that each callback
asks for one delegation. Both the shrinker and the laundromat re-arm
while their condition lasts, so a client with more to give is asked
again on the next pass.

The Linux client ignores craa_objects_to_keep and returns unused
delegations selected from the type mask alone, so the count changes
nothing for it.

Fixes: 44df6f439a17 ("NFSD: add delegation reaper to react to low memory condition")
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260817-recall-any-keep-count-v5-4-3b2cffce701e@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f6da74ce16a9..9d40b573a295 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -7959,6 +7959,7 @@ deleg_reaper(struct nfsd_net *nn)
 {
 	struct list_head *pos, *next;
 	struct nfs4_client *clp;
+	unsigned int count;
 
 	spin_lock(&nn->client_lock);
 	list_for_each_safe(pos, next, &nn->client_lru) {
@@ -7968,21 +7969,33 @@ deleg_reaper(struct nfsd_net *nn)
 			continue;
 		if (clp->cl_state != NFSD4_ACTIVE)
 			continue;
-		if (list_empty(&clp->cl_delegations))
-			continue;
 		if (atomic_read(&clp->cl_delegs_in_recall))
 			continue;
 		if (ktime_get_boottime_seconds() - clp->cl_ra_time < 5)
 			continue;
 		if (clp->cl_cb_state != NFSD4_CB_UP)
 			continue;
+		/*
+		 * This read races with hash_delegation_locked() and
+		 * unhash_delegation_locked() on other CPUs. A stale
+		 * count only skews the keep value; the next
+		 * laundromat pass sees a more current one.
+		 */
+		count = data_race(READ_ONCE(clp->cl_deleg_count));
+		if (!count)
+			continue;
 		if (test_and_set_bit(NFSD4_CALLBACK_RUNNING, &clp->cl_ra->ra_cb.cb_flags))
 			continue;
 
 		/* release in nfsd4_cb_recall_any_release */
 		kref_get(&clp->cl_nfsdfs.cl_ref);
 		clp->cl_ra_time = ktime_get_boottime_seconds();
-		clp->cl_ra->ra_keep = 0;
+		/*
+		 * Ask for a single delegation. Recalling one before it
+		 * is needed costs the client an OPEN when it next
+		 * touches the file.
+		 */
+		clp->cl_ra->ra_keep = count - 1;
 		clp->cl_ra->ra_bmval[0] = BIT(RCA4_TYPE_MASK_RDATA_DLG) |
 						BIT(RCA4_TYPE_MASK_WDATA_DLG) |
 						BIT(RCA4_TYPE_MASK_DIR_DLG);