FAILED: patch "[PATCH] dcache: report a Tasks-RCU quiescent state in dentry_kill()" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x a647a53bc89a046bee4a12a0a5627f2dfaaef807
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

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

From a647a53bc89a046bee4a12a0a5627f2dfaaef807 Mon Sep 17 00:00:00 2001
From: Breno Leitao <[email protected]>
Date: Fri, 18 Sep 2026 04:01:57 -0700
Subject: [PATCH] dcache: report a Tasks-RCU quiescent state in dentry_kill()

I am constantly seeing the following warning on Meta's fleet:

  INFO: rcu_tasks detected stalls on tasks:
    native_queued_spin_lock_slowpath
    locked_inode_to_wb_and_lock_list
    inode_io_list_del
    evict
    __dentry_kill
    shrink_dentry_list
    shrink_dcache_tree
    d_invalidate
    btrfs_delete_subvolume
    btrfs_ioctl_snap_destroy
    btrfs_ioctl
    do_syscall_64

dentry_kill() is the common funnel for dentry teardown: dput(), shrink_dentry_list() and shrink_dcache_tree() all reach it, once per dentry, and its cond_resched() is the only reschedule point on that path.

cond_resched() is not an RCU-tasks quiescent state.

Use cond_resched_tasks_rcu_qs() so the teardown reports an RCU-tasks quiescent state as it proceeds.

---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 8f17db2724b38..e974d42b03e72 100644
@@ -843,7 +843,7 @@ static struct dentry *dentry_kill(struct dentry *dentry)
 	if (dentry->d_op && dentry->d_op->d_release)
 		dentry->d_op->d_release(dentry);
 
-	cond_resched();
+	cond_resched_tasks_rcu_qs();
 	/* now that it's negative, ->d_parent is stable */
 	if (!IS_ROOT(dentry)) {
 		parent = dentry->d_parent;

2.53.0

From: Breno Leitao <[email protected]>

[ Upstream commit a647a53bc89a046bee4a12a0a5627f2dfaaef807 ]

I am constantly seeing the following warning on Meta's fleet:

  INFO: rcu_tasks detected stalls on tasks:
    native_queued_spin_lock_slowpath
    locked_inode_to_wb_and_lock_list
    inode_io_list_del
    evict
    __dentry_kill
    shrink_dentry_list
    shrink_dcache_tree
    d_invalidate
    btrfs_delete_subvolume
    btrfs_ioctl_snap_destroy
    btrfs_ioctl
    do_syscall_64

dentry_kill() is the common funnel for dentry teardown: dput(), shrink_dentry_list() and shrink_dcache_tree() all reach it, once per dentry, and its cond_resched() is the only reschedule point on that path.

cond_resched() is not an RCU-tasks quiescent state.

Use cond_resched_tasks_rcu_qs() so the teardown reports an RCU-tasks quiescent state as it proceeds.

---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index e1f4a9e61e589..023a9ab9c7574 100644
@@ -625,7 +625,7 @@ static void __dentry_kill(struct dentry *dentry)
 	spin_unlock(&dentry->d_lock);
 	if (likely(can_free))
 		dentry_free(dentry);
-	cond_resched();
+	cond_resched_tasks_rcu_qs();
 }
 
 static struct dentry *__lock_parent(struct dentry *dentry)

2.53.0