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From: NeilBrown <neilb@suse.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Thomas Graf <tgraf@suug.ch>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/8] rhashtable: fix race in nested_table_alloc()
Date: Sun, 06 May 2018 07:48:20 +1000	[thread overview]
Message-ID: <871sepepuj.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <20180505092907.2qa3scf6bzvubmtt@gondor.apana.org.au>

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On Sat, May 05 2018, Herbert Xu wrote:

> On Fri, May 04, 2018 at 01:54:14PM +1000, NeilBrown wrote:
>> If two threads run nested_table_alloc() at the same time
>> they could both allocate a new table.
>> Best case is that one of them will never be freed, leaking memory.
>> Worst case is hat entry get stored there before it leaks,
>> and the are lost from the table.
>> 
>> So use cmpxchg to detect the race and free the unused table.
>> 
>> Fixes: da20420f83ea ("rhashtable: Add nested tables")
>> Cc: stable@vger.kernel.org # 4.11+
>> Signed-off-by: NeilBrown <neilb@suse.com>
>
> What about the spinlock that's meant to be held around this
> operation?

The spinlock protects 2 or more buckets.  The nested table contains at
least 512 buckets, maybe more.
It is quite possible for two insertions into 2 different buckets to both
get their spinlock and both try to instantiate the same nested table.

Thanks,
NeilBrown

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  reply	other threads:[~2018-05-05 21:48 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04  3:54 [PATCH 0/8] Assorted rhashtable fixes and cleanups NeilBrown
2018-05-04  3:54 ` [PATCH 1/8] rhashtable: silence RCU warning in rhashtable_test NeilBrown
2018-05-05  9:10   ` Herbert Xu
2018-05-05 21:49     ` NeilBrown
2018-05-04  3:54 ` [PATCH 4/8] rhashtable: fix race in nested_table_alloc() NeilBrown
2018-05-05  9:29   ` Herbert Xu
2018-05-05 21:48     ` NeilBrown [this message]
2018-05-06  5:18       ` Herbert Xu
2018-05-06 22:02         ` NeilBrown
2018-05-04  3:54 ` [PATCH 5/8] rhashtable: remove rhashtable_walk_peek() NeilBrown
2018-05-05  9:30   ` Herbert Xu
2018-05-04  3:54 ` [PATCH 7/8] rhashtable: add rhashtable_walk_prev() NeilBrown
2018-05-05  9:43   ` Herbert Xu
2018-05-05 15:40     ` Tom Herbert
2018-05-06 22:16       ` NeilBrown
2018-05-04  3:54 ` [PATCH 8/8] rhashtable: don't hold lock on first table throughout insertion NeilBrown
2018-05-05  9:41   ` Herbert Xu
2018-05-05 22:00     ` NeilBrown
2018-05-06  5:20       ` Herbert Xu
2018-05-06 22:24         ` NeilBrown
2018-05-07  9:29           ` Herbert Xu
2018-05-08  0:23             ` NeilBrown
2018-05-04  3:54 ` [PATCH 2/8] rhashtable: remove nulls_base and related code NeilBrown
2018-05-05  9:12   ` Herbert Xu
2018-05-05 21:37     ` NeilBrown
2018-05-07  9:27       ` Herbert Xu
2018-05-08  1:14         ` NeilBrown
2018-05-04  3:54 ` [PATCH 3/8] rhashtable: use cmpxchg() to protect ->future_tbl NeilBrown
2018-05-05  9:27   ` Herbert Xu
2018-05-05 21:45     ` NeilBrown
2018-05-04  3:54 ` [PATCH 6/8] rhashtable: further improve stability of rhashtable_walk NeilBrown
2018-05-05  9:42   ` Herbert Xu
2018-05-05 21:50     ` NeilBrown
2018-05-07  9:30       ` Herbert Xu
2018-05-08  0:54         ` NeilBrown
2018-05-04 17:07 ` [PATCH 0/8] Assorted rhashtable fixes and cleanups David Miller

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