[PATCH 5.10.y] dcache: report a Tasks-RCU quiescent state in dentry_kill()

[Sasha Levin <sashal@kernel.org>]

From: Breno Leitao <leitao@debian.org>

[ 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.

Fixes: 9c5f1d30199d ("dcache: move cond_resched() into the end of __dentry_kill()")
Cc: stable@vger.kernel.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260918-dcache-task-rcu-qa-v1-1-963ec83e6d0b@debian.org
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
[ sashal: applied the cond_resched() replacement in __dentry_kill() instead of dentry_kill() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index d17c98508a088..34e8a97e0323e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -595,7 +595,7 @@ 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