From: Minchan Kim <minchan.kim@gmail.com>
To: "Ted Ts'o" <tytso@mit.edu>, Minchan Kim <minchan.kim@gmail.com>,
linux-ext4@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Andreas Dilger <adilger.kernel@dilger.c
Subject: Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage
Date: Mon, 22 Nov 2010 09:38:49 +0900 [thread overview]
Message-ID: <AANLkTimeSWWo-TAJPPH81OO_h1zFzWAT1Gg=XSLyFftH@mail.gmail.com> (raw)
In-Reply-To: <20101121173726.GG23423@thunk.org>
On Mon, Nov 22, 2010 at 2:37 AM, Ted Ts'o <tytso@mit.edu> wrote:
> On Mon, Nov 22, 2010 at 12:39:49AM +0900, Minchan Kim wrote:
>>
>> I think it's no problem.
>>
>> That's because migration always holds lock_page on the file page.
>> So the page couldn't remove from radix.
>
> It may be "ok" in that it won't cause a race, but it still leaves an
> unsightly warning if LOCKDEP is enabled, and LOCKDEP warnings will
> cause /proc_lock_stat to be disabled. So I think it still needs to be
> fixed by adding rcu_read_lock()/rcu_read_unlock() to
> migrate_page_move_mapping().
>
> - Ted
>
Yes. if it is really "ok" about race, we will add rcu_read_lock with
below comment to prevent false positive.
"suppress RCU lockdep false positives".
But I am not sure it's good although rcu_read_lock is little cost.
Whenever we find false positive, should we add rcu_read_lock to
suppress although it's no problem in real product?
Couldn't we provide following function? (or we might have already it
but I missed it. )
/*
* Suppress RCU lockdep false positive.
*/
#ifdef CONFIG_PROVE_RCU
#define rcu_read_lock_suppress rcu_read_lock
#else
#define rcu_read_lock_suppress
#endif
--
Kind regards,
Minchan Kim
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next prev parent reply other threads:[~2010-11-22 0:38 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-21 11:26 [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage Arun Bhanu
2010-11-21 13:30 ` Ted Ts'o
2010-11-21 15:39 ` Minchan Kim
2010-11-21 17:37 ` Ted Ts'o
2010-11-22 0:38 ` Minchan Kim [this message]
2010-11-22 3:31 ` Milton Miller
2010-11-22 6:16 ` Paul E. McKenney
2010-12-07 19:01 ` [BUG?] memory hotplug: include/linux/radix-tree.h:145 invoked rcu_dereference_check() without protection! Gerald Schaefer
2010-12-08 1:19 ` KAMEZAWA Hiroyuki
2010-12-16 13:50 ` Gerald Schaefer
2010-12-17 0:04 ` Minchan Kim
2010-12-17 5:47 ` Paul E. McKenney
2010-12-17 5:59 ` Eric Dumazet
2010-12-17 15:08 ` Minchan Kim
2010-12-17 16:03 ` Paul E. McKenney
2010-12-17 8:39 ` Mel Gorman
2010-12-17 9:28 ` Mel Gorman
2010-12-17 15:22 ` Minchan Kim
2010-12-17 15:13 ` Minchan Kim
2010-12-17 16:01 ` Paul E. McKenney
2010-11-23 7:16 ` [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage KOSAKI Motohiro
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