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From: Andre Noll <maan@systemlinux.org>
To: Neil Brown <neilb@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
	"K.Tanaka" <k-tanaka@ce.jp.nec.com>
Subject: Re: [PATCH 001 of 9] md: Fix deadlock in md/raid1 and md/raid10 when handling a read error.
Date: Tue, 4 Mar 2008 12:29:45 +0100	[thread overview]
Message-ID: <20080304112945.GB32242@skl-net.de> (raw)
In-Reply-To: <18380.59250.90214.461186@notabene.brown>

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On 17:08, Neil Brown wrote:
> > Do we really need to take the spin lock in the common case where
> > conf->pending_bio_list.head is NULL? If not, the above could be
> > optimized to the slightly faster and better readable
> > 
> > 	struct bio *bio;
> > 
> > 	if (!conf->pending_bio_list.head)
> > 		return 0;
> > 	spin_lock_irq(&conf->device_lock);
> > 	bio = bio_list_get(&conf->pending_bio_list);
> > 	...
> > 	spin_unlock_irq(&conf->device_lock);
> > 	return 1;
> 
> Maybe... If I write a memory location inside a spinlock, then after
> the spinlock is dropped, I read that location on a different CPU,
> am I always guaranteed to see the new value? or do I need some sort of
> memory barrier?

Are you worried about another CPU setting conf->pending_bio_list.head
to != NULL after the if statement? If that's an issue I think also
the original patch is problematic because the same might happen after
the final spin_unlock_irq() but but before flush_pending_writes()
returns zero.

Andre
-- 
The only person who always got his work done by Friday was Robinson Crusoe

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  reply	other threads:[~2008-03-04 11:30 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-03  0:16 [PATCH 000 of 9] md: Introduction EXPLAIN PATCH SET HERE NeilBrown
2008-03-03  0:17 ` [PATCH 001 of 9] md: Fix deadlock in md/raid1 and md/raid10 when handling a read error NeilBrown
2008-03-03 15:54   ` Andre Noll
2008-03-04  6:08     ` Neil Brown
2008-03-04 11:29       ` Andre Noll [this message]
2008-03-06  3:29         ` Neil Brown
2008-03-06 10:51           ` Andre Noll
2008-03-03  0:17 ` [PATCH 002 of 9] md: Reduce CPU wastage on idle md array with a write-intent bitmap NeilBrown
2008-03-03  0:17 ` [PATCH 003 of 9] md: Guard against possible bad array geometry in v1 metadata NeilBrown
2008-03-03  0:17 ` [PATCH 004 of 9] md: Clean up irregularity with raid autodetect NeilBrown
2008-03-03  0:17 ` [PATCH 005 of 9] md: Make sure a reshape is started when device switches to read-write NeilBrown
2008-03-03  0:17 ` [PATCH 006 of 9] md: Lock access to rdev attributes properly NeilBrown
2008-03-03  0:17 ` [PATCH 007 of 9] md: Don't attempt read-balancing for raid10 'far' layouts NeilBrown
2008-03-03  0:17 ` [PATCH 008 of 9] md: Fix possible raid1/raid10 deadlock on read error during resync NeilBrown
2008-03-03  0:18 ` [PATCH 009 of 9] md: The md RAID10 resync thread could cause a md RAID10 array deadlock NeilBrown

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