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Re: [patch] mm: fix lockless pagecache reordering bug (was Re: BUG: soft

To: Nick Piggin <npiggin@xxxxxxx>
Subject: Re: [patch] mm: fix lockless pagecache reordering bug (was Re: BUG: soft lockup - is this XFS problem?)
From: Roman Kononov <kononov@xxxxxxxx>
Date: Tue, 06 Jan 2009 10:16:32 -0600
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Peter Klotz <peter.klotz@xxxxxx>, stable@xxxxxxxxxx, Linux Memory Management List <linux-mm@xxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Roman Kononov <kernel@xxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
In-reply-to: <20090106020550.GA819@xxxxxxxxxxxxx>
Newsgroups: gmane.linux.kernel.mm, gmane.linux.kernel
References: <20090105041959.GC367@xxxxxxxxxxxxx> <20090105064838.GA5209@xxxxxxxxxxxxx> <49623384.2070801@xxxxxx> <20090105164135.GC32675@xxxxxxxxxxxxx> <alpine.LFD.2.00.0901050859430.3057@xxxxxxxxxxxxxxxxxxxxx> <20090105180008.GE32675@xxxxxxxxxxxxx> <alpine.LFD.2.00.0901051027011.3057@xxxxxxxxxxxxxxxxxxxxx> <20090105201258.GN6959@xxxxxxxxxxxxxxxxxx> <alpine.LFD.2.00.0901051224110.3057@xxxxxxxxxxxxxxxxxxxxx> <20090105215727.GQ6959@xxxxxxxxxxxxxxxxxx> <20090106020550.GA819@xxxxxxxxxxxxx>
User-agent: Thunderbird 2.0.0.18 (X11/20081125)
On 2009-01-05 20:05 Nick Piggin said the following:
Subject: mm lockless pagecache barrier fix
 static inline void *radix_tree_deref_slot(void **pslot)
 {
-       void *ret = *pslot;
+       void *ret = rcu_dereference(*pslot);
        if (unlikely(radix_tree_is_indirect_ptr(ret)))
                ret = RADIX_TREE_RETRY;
        return ret;

3 systems are working fine for a few hours with the patch. They would fail within 20 minutes without it.

Thanks.

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