From: KOSAKI Motohiro Subject: Re: [BUG?] [Ext4] INFO: suspicious rcu_dereference_check() usage Date: Tue, 23 Nov 2010 16:16:56 +0900 (JST) Message-ID: <20101122174516.E24A.A69D9226@jp.fujitsu.com> References: <20101121153949.GD20947@barrios-desktop> <20101121173726.GG23423@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-2022-JP" Content-Transfer-Encoding: 7bit Cc: kosaki.motohiro@jp.fujitsu.com To: "Ted Ts'o" , Minchan Kim , linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andreas Dilger In-Reply-To: <20101121173726.GG23423@thunk.org> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org > 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(). Hi Ted, Current mmotm has following patch and I think it should be fixed your issue. Thanks. From: Zeng Zhaoming find_task_by_vpid() should be protected by rcu_read_lock(), to prevent free_pid() reclaiming pid. Signed-off-by: Zeng Zhaoming Cc: "Paul E. McKenney" Cc: KOSAKI Motohiro Cc: Christoph Lameter Signed-off-by: Andrew Morton --- mm/mempolicy.c | 3 +++ 1 file changed, 3 insertions(+) diff -puN mm/mempolicy.c~mm-mempolicyc-add-rcu-read-lock-to-protect-pid-structure mm/mempolicy.c --- a/mm/mempolicy.c~mm-mempolicyc-add-rcu-read-lock-to-protect-pid-structure +++ a/mm/mempolicy.c @@ -1307,15 +1307,18 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pi goto out; /* Find the mm_struct */ + rcu_read_lock(); read_lock(&tasklist_lock); task = pid ? find_task_by_vpid(pid) : current; if (!task) { read_unlock(&tasklist_lock); + rcu_read_unlock(); err = -ESRCH; goto out; } mm = get_task_mm(task); read_unlock(&tasklist_lock); + rcu_read_unlock(); -- 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: email@kvack.org