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Re: [PATCH v2] rhashtable: Kill harmless RCU warning in rhashtable_walk_init

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From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Sat, 19 Dec 2015 10:45:28 +0800

> On Fri, Dec 18, 2015 at 04:27:31PM -0500, David Miller wrote:
>> From: Herbert Xu <herbert@gondor.apana.org.au>
>> Date: Fri, 18 Dec 2015 21:14:08 +0800
>> 
>> > On Fri, Dec 18, 2015 at 04:54:14AM -0800, Eric Dumazet wrote:
>> >>
>> >> You can avoid the comment by using the self documented and lockdep
>> >> enabled primitive
>> >> 
>> >> iter->walker->tbl = rcu_dereference_protected(ht->tbl,
>> >> 					      lockdep_is_held(&ht->lock));
>> > 
>> > That is just gross.  I think a comment is much better in this case.
>> 
>> Herbert, this macro was created exactly to handle this situation,
>> and this is what we do everywhere else in the tree.
> 
> OK.
> 
> ---8<---
> The commit f9f51b8070be3e829100614a7372b219723b864f ("rhashtable:
> Fix walker list corruption") causes a suspicious RCU usage warning
> because we no longer hold ht->mutex when we dereference ht->tbl.
> 
> However, this is a false positive because we now hold ht->lock
> which also guarantees that ht->tbl won't disppear from under us.
> 
> This patch kills the warning by using rcu_dereference_protected.
> 
> Reported-by: kernel test robot <ying.huang@linux.intel.com>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

The correct commti SHA1 is c6ff5268293ef98e48a99597e765ffc417e39fa5.

Or at least, when I run:

	git show f9f51b8070be3e829100614a7372b219723b864f

I get:

	fatal: bad object f9f51b8070be3e829100614a7372b219723b864f

:-)

I fixed this up and applied this, thanks!
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Re: [lkp] [rhashtable] f9f51b8070: INFO: suspicious RCU usage. ] Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 06:40 +0100
  rhashtable: Kill harmless RCU warning in rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 07:30 +0100
    Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init Eric Dumazet <eric.dumazet@gmail.com> - 2015-12-18 14:00 +0100
      Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-18 14:20 +0100
        Re: rhashtable: Kill harmless RCU warning in rhashtable_walk_init David Miller <davem@davemloft.net> - 2015-12-18 22:30 +0100
          [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init Herbert Xu <herbert@gondor.apana.org.au> - 2015-12-19 03:50 +0100
            Re: [LKP] [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init Fengguang Wu <fengguang.wu@intel.com> - 2015-12-19 05:50 +0100
            Re: [PATCH v2] rhashtable: Kill harmless RCU warning in  rhashtable_walk_init David Miller <davem@davemloft.net> - 2015-12-19 05:50 +0100

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