On Wed, 11 Feb 2015 03:15:37 +0000
Ben Hutchings <ben@xxxxxxxxxxxxxxx> wrote:
> I've reviewed locking contexts in all three functions that I changed
> when backporting "deal with deadlock in d_walk()". It's actually worse
> than you say:
>
> - We don't hold this_parent->d_lock at the 'positive' label in
> have_submounts(), but it is unlocked after 'rename_retry'.
> - There is an rcu_read_unlock() after the 'out' label in
> select_parent(), but it's not held at the 'goto out'.
>
> Does the following patch work for you?
I booted the original 3.2 kernel 3 times and it succeeded once, and
crashed the other two.
I applied this patch and booted it 5 times, and it succeeded every time.
I removed the patch, and it crashed on the very next boot.
Thus, I'd say it seems to have fixed the issue for me.
Tested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
-- Steve
>
> Ben.
>
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -1035,7 +1035,7 @@ ascend:
> return 0; /* No mount points found in tree */
> positive:
> if (!locked && read_seqretry(&rename_lock, seq))
> - goto rename_retry;
> + goto rename_retry_unlocked;
> if (locked)
> write_sequnlock(&rename_lock);
> return 1;
> @@ -1045,6 +1045,7 @@ rename_retry:
> rcu_read_unlock();
> if (locked)
> goto again;
> +rename_retry_unlocked:
> locked = 1;
> write_seqlock(&rename_lock);
> goto again;
> @@ -1109,6 +1110,7 @@ resume:
> */
> if (found && need_resched()) {
> spin_unlock(&dentry->d_lock);
> + rcu_read_lock();
> goto out;
> }
>
> --- END ---
>
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