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.ca>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Eric Sandeen <sandeen@redhat.com>
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
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-11-22 0:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20101121112611.GB4267@deepthought.bhanu.net>
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]
2010-11-23 7:16 ` KOSAKI Motohiro
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='AANLkTimeSWWo-TAJPPH81OO_h1zFzWAT1Gg=XSLyFftH@mail.gmail.com' \
--to=minchan.kim@gmail.com \
--cc=adilger.kernel@dilger.ca \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=sandeen@redhat.com \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox