linux-kernel - Re: FW: [PATCH 008 of 9] md: Fix possible raid1/raid10 deadlock on read error during resync.

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Date:	Mon, 24 Mar 2008 13:49:03 -0500
From:	"John Z." <md2sf@...l.com>
To:	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: FW: [PATCH 008 of 9] md: Fix possible raid1/raid10 deadlock on
 read error during resync.


> 
> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org
> [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of NeilBrown
> Sent: Sunday, March 02, 2008 5:18 PM
> To: Andrew Morton
> Cc: linux-raid@...r.kernel.org; linux-kernel@...r.kernel.org; K.Tanaka
> Subject: [PATCH 008 of 9] md: Fix possible raid1/raid10 deadlock on read
> error during resync.
> 

> diff .prev/drivers/md/raid1.c ./drivers/md/raid1.c
> --- .prev/drivers/md/raid1.c	2008-03-03 11:03:39.000000000 +1100
> +++ ./drivers/md/raid1.c	2008-03-03 09:56:52.000000000 +1100
> @@ -704,13 +704,20 @@ static void freeze_array(conf_t *conf)
>   	/* stop syncio and normal IO and wait for everything to
>   	 * go quite.
>   	 * We increment barrier and nr_waiting, and then
> -	 * wait until barrier+nr_pending match nr_queued+2
> +	 * wait until nr_pending match nr_queued+1
> +	 * This is called in the context of one normal IO request
> +	 * that has failed. Thus any sync request that might be pending
> +	 * will be blocked by nr_pending, and we need to wait for
> +	 * pending IO requests to complete or be queued for re-try.
> +	 * Thus the number queued (nr_queued) plus this request (1)
> +	 * must match the number of pending IOs (nr_pending) before
> +	 * we continue.
>   	 */
>   	spin_lock_irq(&conf->resync_lock);
>   	conf->barrier++;
>   	conf->nr_waiting++;
>   	wait_event_lock_irq(conf->wait_barrier,
> -			    conf->barrier+conf->nr_pending ==
> conf->nr_queued+2,
> +			    conf->nr_pending == conf->nr_queued+1,
>   			    conf->resync_lock,
>   			    ({ flush_pending_writes(conf);
>   			       raid1_unplug(conf->mddev->queue); }));
> --

When we call freeze_array, it is after reschedule_retry, during which conf->nr_queued is already incremented.
Should we use conf->nr_pending == conf->nr_pending here?




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