FAILED: patch "[PATCH] nfsd: fix BUG_ON in nfsd4_alloc_layout_stateid on racing" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-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-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x ca94ba36172046be6a694a7986f6931e47ed4d51
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090305-settle-sarcasm-3f00@gregkh' --subject-prefix 'PATCH 6.1.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 <[email protected]>
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.

index f34320e4c2f4..1de2f6cd1f09 100644
@@ -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;

From: Jeff Layton <[email protected]>

[ 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.

---
 fs/nfsd/nfs4layouts.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

index 84bb200e24ade..03c8e71d1974a 100644
@@ -168,9 +168,12 @@ 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);

@@ -235,11 +238,17 @@ 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