FAILED: patch "[PATCH] nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x ca94ba36172046be6a694a7986f6931e47ed4d51
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026090305-musky-peculiar-c632@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From ca94ba36172046be6a694a7986f6931e47ed4d51 Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton@kernel.org>
Date: Sat, 30 May 2026 09:19:17 -0400
Subject: [PATCH] nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing
 delegation revoke

nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding
fi_lock when the parent stateid is a delegation. A concurrent delegation
revoke via the laundromat can clear fi_deleg_file under fi_lock, causing
nfsd_file_get() to return NULL and triggering the BUG_ON.

This race is client-reachable: two NFS clients can trigger it by having
one hold a delegation while another opens the same file to force a
recall. When the first client doesn't respond to the recall, the
laundromat revokes it. A concurrent LAYOUTGET from any client using the
delegation stateid hits the race window.

Fix this by taking fi_lock around the fi_deleg_file read in the
SC_TYPE_DELEG path, matching the locking discipline of the
find_any_file() arm, and replacing the BUG_ON with a graceful error
return that cleans up the partially-initialized layout stateid.

Fixes: c5c707f96fc9 ("nfsd: implement pNFS layout recalls")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-1-f27e8eb4d974@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
index f34320e4c2f4..1de2f6cd1f09 100644
--- a/fs/nfsd/nfs4layouts.c
+++ b/fs/nfsd/nfs4layouts.c
@@ -247,11 +247,17 @@ nfsd4_alloc_layout_stateid(struct nfsd4_compound_state *cstate,
 	nfsd4_init_cb(&ls->ls_recall, clp, &nfsd4_cb_layout_ops,
 			NFSPROC4_CLNT_CB_LAYOUT);
 
-	if (parent->sc_type == SC_TYPE_DELEG)
+	if (parent->sc_type == SC_TYPE_DELEG) {
+		spin_lock(&fp->fi_lock);
 		ls->ls_file = nfsd_file_get(fp->fi_deleg_file);
-	else
+		spin_unlock(&fp->fi_lock);
+	} else {
 		ls->ls_file = find_any_file(fp);
-	BUG_ON(!ls->ls_file);
+	}
+	if (!ls->ls_file) {
+		nfs4_put_stid(stp);
+		return NULL;
+	}
 
 	ls->ls_fenced = false;
 	ls->ls_fence_delay = 0;

[PATCH 5.15.y] nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing delegation revoke

[Sasha Levin]

From: Jeff Layton <jlayton@kernel.org>

[ Upstream commit ca94ba36172046be6a694a7986f6931e47ed4d51 ]

nfsd4_alloc_layout_stateid reads fp->fi_deleg_file without holding
fi_lock when the parent stateid is a delegation. A concurrent delegation
revoke via the laundromat can clear fi_deleg_file under fi_lock, causing
nfsd_file_get() to return NULL and triggering the BUG_ON.

This race is client-reachable: two NFS clients can trigger it by having
one hold a delegation while another opens the same file to force a
recall. When the first client doesn't respond to the recall, the
laundromat revokes it. A concurrent LAYOUTGET from any client using the
delegation stateid hits the race window.

Fix this by taking fi_lock around the fi_deleg_file read in the
SC_TYPE_DELEG path, matching the locking discipline of the
find_any_file() arm, and replacing the BUG_ON with a graceful error
return that cleans up the partially-initialized layout stateid.

Fixes: c5c707f96fc9 ("nfsd: implement pNFS layout recalls")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-1-f27e8eb4d974@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfsd/nfs4layouts.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
index bcf16dd07d488..d0b76aee54f83 100644
--- a/fs/nfsd/nfs4layouts.c
+++ b/fs/nfsd/nfs4layouts.c
@@ -167,9 +167,12 @@ nfsd4_free_layout_stateid(struct nfs4_stid *stid)
 	list_del_init(&ls->ls_perfile);
 	spin_unlock(&fp->fi_lock);
 
-	if (!nfsd4_layout_ops[ls->ls_layout_type]->disable_recalls)
-		vfs_setlease(ls->ls_file->nf_file, F_UNLCK, NULL, (void **)&ls);
-	nfsd_file_put(ls->ls_file);
+	if (ls->ls_file) {
+		if (!nfsd4_layout_ops[ls->ls_layout_type]->disable_recalls)
+			vfs_setlease(ls->ls_file->nf_file, F_UNLCK, NULL,
+				     (void **)&ls);
+		nfsd_file_put(ls->ls_file);
+	}
 
 	if (ls->ls_recalled)
 		atomic_dec(&ls->ls_stid.sc_file->fi_lo_recalls);
@@ -234,11 +237,17 @@ nfsd4_alloc_layout_stateid(struct nfsd4_compound_state *cstate,
 	nfsd4_init_cb(&ls->ls_recall, clp, &nfsd4_cb_layout_ops,
 			NFSPROC4_CLNT_CB_LAYOUT);
 
-	if (parent->sc_type == NFS4_DELEG_STID)
+	if (parent->sc_type == NFS4_DELEG_STID) {
+		spin_lock(&fp->fi_lock);
 		ls->ls_file = nfsd_file_get(fp->fi_deleg_file);
-	else
+		spin_unlock(&fp->fi_lock);
+	} else {
 		ls->ls_file = find_any_file(fp);
-	BUG_ON(!ls->ls_file);
+	}
+	if (!ls->ls_file) {
+		nfs4_put_stid(stp);
+		return NULL;
+	}
 
 	if (nfsd4_layout_setlease(ls)) {
 		nfs4_put_stid(stp);
-- 
2.53.0