Re: [git pull] Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667]

[Linus Torvalds]

On Sat, 31 May 2014, Josh Boyer wrote:
> 
> One of my machines got the lockdep report below when booting a kernel
> that contained these patches. 

I think this is just a lacking annotation.

We do nest dentry d_lock locking, and in order to avoid ABBA deadlocks the 
rule is that we lock things in topological order (parent dentry first). 
lock_parent() is very careful about that, but doesn't actually tell 
lockdep about it.

This trivial oneliner should fix it.

			Linus

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

diff --git a/fs/dcache.c b/fs/dcache.c
index bce851dc03ef..be2bea834bf4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -553,7 +553,7 @@ again:
 	}
 	rcu_read_unlock();
 	if (parent != dentry)
-		spin_lock(&dentry->d_lock);
+		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 	else
 		parent = NULL;
 	return parent;
--
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