linux-kernel - Re: [PATCH 05/17] writeback: quit throttling when signal pending

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100914091720.GA23042@localhost>
Date:	Tue, 14 Sep 2010 17:17:20 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Neil Brown <neilb@...e.de>, linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Theodore Ts'o <tytso@....edu>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	Chris Mason <chris.mason@...cle.com>,
	Christoph Hellwig <hch@....de>,
	"Li, Shaohua" <shaohua.li@...el.com>
Subject: Re: [PATCH 05/17] writeback: quit throttling when signal pending

On Tue, Sep 14, 2010 at 04:44:37PM +0800, KOSAKI Motohiro wrote:
> > On Tue, Sep 14, 2010 at 04:23:56PM +0800, KOSAKI Motohiro wrote:
> > > > Subject: writeback: quit throttling when fatal signal pending
> > > > From: Wu Fengguang <fengguang.wu@...el.com>
> > > > Date: Wed Sep 08 17:40:22 CST 2010
> > > > 
> > > > This allows quick response to Ctrl-C etc. for impatient users.
> > > > 
> > > > It mainly helps the rare bdi/global dirty exceeded cases.
> > > > In the normal case of not exceeded, it will quit the loop anyway. 
> > > > 
> > > > CC: Neil Brown <neilb@...e.de>
> > > > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > > > ---
> > > >  mm/page-writeback.c |    3 +++
> > > >  1 file changed, 3 insertions(+)
> > > > 
> > > > --- linux-next.orig/mm/page-writeback.c	2010-09-12 13:25:23.000000000 +0800
> > > > +++ linux-next/mm/page-writeback.c	2010-09-13 11:39:33.000000000 +0800
> > > > @@ -552,6 +552,9 @@ static void balance_dirty_pages(struct a
> > > >  		__set_current_state(TASK_INTERRUPTIBLE);
> > > >  		io_schedule_timeout(pause);
> > > >  
> > > > +		if (fatal_signal_pending(current))
> > > > +			break;
> > > > +
> > > >  check_exceeded:
> > > >  		/*
> > > >  		 * The bdi thresh is somehow "soft" limit derived from the
> > > 
> > > I think we need to change callers (e.g. generic_perform_write) too.
> > > Otherwise, plenty write + SIGKILL combination easily exceed dirty limit.
> > > It mean we can see strange OOM.
> > 
> > If it's dangerous, we can do without this patch.  
> 
> How?

As you described.

> > The users can still
> > get quick response in normal case after all.
> > 
> > However, I suspect the process is guaranteed to exit on
> > fatal_signal_pending, so it won't dirty more pages :)
> 
> Process exiting is delayed until syscall exiting. So, we exit write syscall
> manually if necessary.

Got it, you mean this fix. It looks good. I didn't add "status =
-EINTR" in the patch because the bottom line "written ? : status" will
always select the non-zero written.

diff --git a/mm/filemap.c b/mm/filemap.c
index 3d4df44..f6d2740 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2304,7 +2304,8 @@ again:
 		written += copied;
 
 		balance_dirty_pages_ratelimited(mapping);
-
+		if (fatal_signal_pending(current))
+			break;
 	} while (iov_iter_count(i));
 
 	return written ? written : status;

Thanks,
Fengguang
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/