linux-kernel - Re: [patch] mm: fix lockless pagecache reordering bug (was Re: BUG: soft lockup

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Message-ID: <20090106084312.GC16738@wotan.suse.de>
Date:	Tue, 6 Jan 2009 09:43:12 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Peter Klotz <peter.klotz@....at>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org,
	Linux Memory Management List <linux-mm@...ck.org>,
	Christoph Hellwig <hch@...radead.org>,
	Roman Kononov <kernel@...onov.ftml.net>,
	linux-kernel@...r.kernel.org, xfs@....sgi.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch] mm: fix lockless pagecache reordering bug (was Re: BUG: soft lockup - is this XFS problem?)

On Tue, Jan 06, 2009 at 09:38:15AM +0100, Peter Klotz wrote:
> >Index: linux-2.6/include/linux/radix-tree.h
> >===================================================================
> >--- linux-2.6.orig/include/linux/radix-tree.h
> >+++ linux-2.6/include/linux/radix-tree.h
> >@@ -136,7 +136,7 @@ do {						 \
> >  */
> > 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;
> >
> >
> 
> The patch above fixes my problem. I did two complete test runs that 
> normally fail rather quickly.

OK, thanks for reporting and testing. 

I think this patch is a candidate for -stable too.

Thanks,
Nick
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