On 06/16, Peter Zijlstra wrote:
>
>
> I made that the below.
>
> Are you OK with the Changelog edits and the added SoB ?
Of course,
Thanks Peter!
Oleg.
> ---
> Subject: perf: Fix ring_buffer_attach() RCU sync, again.
> From: Oleg Nesterov <o...@redhat.com>
> Date: Sat, 30 May 2015 22:04:25 +0200
>
> While looking for other users of get_state/cond_sync. I Found
> ring_buffer_attach() and it looks obviously buggy?
>
> Don't we need to ensure that we have "synchronize" _between_
> list_del() and list_add() ?
>
> IOW. Suppose that ring_buffer_attach() preempts right_after
> get_state_synchronize_rcu() and gp completes before spin_lock().
>
> In this case cond_synchronize_rcu() does nothing and we reuse
> ->rb_entry without waiting for gp in between?
>
> It also moves the ->rcu_pending check under "if (rb)", to make it
> more readable imo.
>
> Cc: t...@kernel.org
> Cc: mi...@redhat.com
> Cc: der.h...@hofr.at
> Cc: d...@stgolabs.net
> Cc: torva...@linux-foundation.org
> Cc: j...@joshtriplett.org
> Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
> Fixes: b69cf53640da ("perf: Fix a race between ring_buffer_detach() and
> ring_buffer_attach()")
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> Link: http://lkml.kernel.org/r/20150530200425.ga15...@redhat.com
> ---
> kernel/events/core.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4307,20 +4307,20 @@ static void ring_buffer_attach(struct pe
> WARN_ON_ONCE(event->rcu_pending);
>
> old_rb = event->rb;
> - event->rcu_batches = get_state_synchronize_rcu();
> - event->rcu_pending = 1;
> -
> spin_lock_irqsave(&old_rb->event_lock, flags);
> list_del_rcu(&event->rb_entry);
> spin_unlock_irqrestore(&old_rb->event_lock, flags);
> - }
>
> - if (event->rcu_pending && rb) {
> - cond_synchronize_rcu(event->rcu_batches);
> - event->rcu_pending = 0;
> + event->rcu_batches = get_state_synchronize_rcu();
> + event->rcu_pending = 1;
> }
>
> if (rb) {
> + if (event->rcu_pending) {
> + cond_synchronize_rcu(event->rcu_batches);
> + event->rcu_pending = 0;
> + }
> +
> spin_lock_irqsave(&rb->event_lock, flags);
> list_add_rcu(&event->rb_entry, &rb->event_list);
> spin_unlock_irqrestore(&rb->event_lock, flags);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
