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

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Date:	Sat, 31 May 2014 12:12:18 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [git pull] Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for
 22s! [systemd-udevd:1667]

On Sat, May 31, 2014 at 10:48 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>
> 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

Built the previous kernel with just this applied and it seems to
behave correctly on several reboots.  I think this looks good.
Thanks!

josh

>
> ---
>  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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