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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Markus Pargmann <mpa@pengutronix.de>
Cc: nbd-general@lists.sourceforge.net,
	Oleg Nesterov <oleg@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] nbd: Remove signal usage
Date: Tue, 10 Nov 2015 04:46:18 +0000	[thread overview]
Message-ID: <20151110044617.GC22011@ZenIV.linux.org.uk> (raw)
In-Reply-To: <1446133360-30652-2-git-send-email-mpa@pengutronix.de>

On Thu, Oct 29, 2015 at 04:42:37PM +0100, Markus Pargmann wrote:
>  	del_timer_sync(&nbd->timeout_timer);
> +
> +out:
> +	spin_unlock_irq(&nbd->sock_lock);

... and in its callback we have this:

> @@ -148,17 +155,15 @@ static void nbd_xmit_timeout(unsigned long arg)
>  
>  	nbd->disconnect = true;
>  
> -	spin_lock_irqsave(&nbd->tasks_lock, flags);
> +	spin_lock_irqsave(&nbd->sock_lock, flags);

* CPU 1 enters sock_shutdown() and grabs ->sock_lock.
* on CPU2 the timer hits and we enter the callback, where we spin on that
spinlock.
* in the meanwhile, CPU1 calls del_timer_sync()

Deadlock...

  reply	other threads:[~2015-11-10  4:46 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-29 15:42 [PATCH 0/4] nbd: Remove signal usage Markus Pargmann
2015-10-29 15:42 ` [PATCH 1/4] " Markus Pargmann
2015-11-10  4:46   ` Al Viro [this message]
2015-11-10 10:22     ` Markus Pargmann
2015-10-29 15:42 ` [PATCH 2/4] nbd: Timeouts are not user requested disconnects Markus Pargmann
2015-10-29 15:42 ` [PATCH 3/4] nbd: Cleanup reset of nbd and bdev after a disconnect Markus Pargmann
2015-10-29 15:42 ` [PATCH 4/4] nbd: Move flag parsing to a function Markus Pargmann
2015-11-01 19:05 ` [PATCH 0/4] nbd: Remove signal usage Oleg Nesterov
2015-11-09 11:09   ` Markus Pargmann

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