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From: Phil Sutter <phil@nwl.cc>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, tgraf@suug.ch,
	fengguang.wu@intel.com, wfg@linux.intel.com, lkp@01.org
Subject: Re: rhashtable: Prevent spurious EBUSY errors on insertion
Date: Thu, 3 Dec 2015 16:38:05 +0100	[thread overview]
Message-ID: <20151203153805.GC17467@orbit.nwl.cc> (raw)
In-Reply-To: <20151203124129.GA5505@gondor.apana.org.au>

On Thu, Dec 03, 2015 at 08:41:29PM +0800, Herbert Xu wrote:
> On Mon, Nov 30, 2015 at 06:18:59PM +0800, Herbert Xu wrote:
> > 
> > OK that's better.  I think I see the problem.  The test in
> > rhashtable_insert_rehash is racy and if two threads both try
> > to grow the table one of them may be tricked into doing a rehash
> > instead.
> > 
> > I'm working on a fix.
> 
> OK this patch fixes the EBUSY problem as far as I can tell.  Please
> let me know if you still observe EBUSY with it.  I'll respond to the
> ENOMEM problem in another email.
> 
> ---8<---
> Thomas and Phil observed that under stress rhashtable insertion
> sometimes failed with EBUSY, even though this error should only
> ever been seen when we're under attack and our hash chain length
> has grown to an unacceptable level, even after a rehash.
> 
> It turns out that the logic for detecting whether there is an
> existing rehash is faulty.  In particular, when two threads both
> try to grow the same table at the same time, one of them may see
> the newly grown table and thus erroneously conclude that it had
> been rehashed.  This is what leads to the EBUSY error.
> 
> This patch fixes this by remembering the current last table we
> used during insertion so that rhashtable_insert_rehash can detect
> when another thread has also done a resize/rehash.  When this is
> detected we will give up our resize/rehash and simply retry the
> insertion with the new table.
> 
> Reported-by: Thomas Graf <tgraf@suug.ch>
> Reported-by: Phil Sutter <phil@nwl.cc>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Tested-by: Phil Sutter <phil@nwl.cc>

  reply	other threads:[~2015-12-03 15:38 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-20 17:17 [PATCH v2 0/4] improve fault-tolerance of rhashtable runtime-test Phil Sutter
2015-11-20 17:17 ` [PATCH v2 1/4] rhashtable-test: add cond_resched() to thread test Phil Sutter
2015-11-20 17:17 ` [PATCH v2 2/4] rhashtable-test: retry insert operations Phil Sutter
2015-11-20 17:17 ` [PATCH v2 3/4] rhashtable-test: calculate max_entries value by default Phil Sutter
2015-11-20 17:17 ` [PATCH v2 4/4] rhashtable-test: allow to retry even if -ENOMEM was returned Phil Sutter
2015-11-20 17:28   ` Phil Sutter
2015-11-23 17:38 ` [PATCH v2 0/4] improve fault-tolerance of rhashtable runtime-test David Miller
2015-11-30  9:37 ` Herbert Xu
2015-11-30 10:14   ` Phil Sutter
2015-11-30 10:18     ` Herbert Xu
2015-12-03 12:41       ` rhashtable: Prevent spurious EBUSY errors on insertion Herbert Xu
2015-12-03 15:38         ` Phil Sutter [this message]
2015-12-04 19:38         ` David Miller
2015-12-17  8:46         ` Xin Long
2015-12-17  8:48           ` Herbert Xu
2015-12-17  9:00             ` Xin Long
2015-12-17 16:07               ` Xin Long
2015-12-18  2:26                 ` Herbert Xu
2015-12-18  8:18                   ` Xin Long
2015-12-17 17:00               ` David Miller
2015-12-03 12:51       ` rhashtable: ENOMEM errors when hit with a flood of insertions Herbert Xu
2015-12-03 15:08         ` David Laight
2015-12-03 16:08         ` Eric Dumazet
2015-12-04  0:07           ` Herbert Xu
2015-12-04 14:39           ` rhashtable: Use __vmalloc with GFP_ATOMIC for table allocation Herbert Xu
2015-12-04 17:01             ` Phil Sutter
2015-12-04 17:45               ` Eric Dumazet
2015-12-04 18:15                 ` Phil Sutter
2015-12-05  7:06                   ` Herbert Xu
2015-12-07 15:35                     ` Thomas Graf
2015-12-07 19:29                       ` David Miller
2015-12-09  2:18                     ` Thomas Graf
2015-12-09  2:24                       ` Herbert Xu
2015-12-09  2:36                         ` Thomas Graf
2015-12-09  2:38                           ` Herbert Xu
2015-12-09  2:42                             ` Thomas Graf
2015-12-04 21:53             ` David Miller
2015-12-05  7:03               ` Herbert Xu
2015-12-06  3:48                 ` David Miller

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