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Date:	Thu, 13 Aug 2015 14:30:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] inet: fix races with reqsk timers

On Fri, 2015-08-14 at 00:13 +0300, Nikolay Aleksandrov wrote:
> > On Aug 13, 2015, at 11:44 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > 
> > On Thu, 2015-08-13 at 13:19 -0700, Eric Dumazet wrote:
> > 
> >> 
> >> A caller handler can not call del_timer_sync()
> > 
> > A timer handler can not call del_timer_sync()
> > 
> > I am testing a minimal fix :
> > 
> > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > index 05e3145f7dc3..134957159c27 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -593,7 +593,7 @@ static bool reqsk_queue_unlink(struct request_sock_queue *queue,
> > 	}
> > 
> > 	spin_unlock(&queue->syn_wait_lock);
> > -	if (del_timer_sync(&req->rsk_timer))
> > +	if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer))
> > 		reqsk_put(req);
> > 	return found;
> > }
> > 
> > 
> 
> Wouldn’t try_to_del_timer_sync(&req->rsk_timer) > 0 be better ?

I am not sure : there are contexts where we need to wait for the timer
being completed (this was point of commit
2235f2ac75fd2501c251b0b699a9632e80239a6d)

(problem is that timer handler can rearm itself)



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