From: Jan Kara Subject: Re: [PATCH] jbd_commit_transaction() races with journal_try_to_drop_buffers() causing DIO failures Date: Wed, 14 May 2008 19:08:56 +0200 Message-ID: <20080514170856.GH24363@duck.suse.cz> References: <20080428180932.GI17054@duck.suse.cz> <1209409764.11872.6.camel@localhost.localdomain> <20080429124321.GD1987@duck.suse.cz> <1209654981.27240.19.camel@badari-desktop> <20080505170636.GK25722@duck.suse.cz> <1210372072.3639.52.camel@localhost.localdomain> <20080512155419.GD15856@duck.suse.cz> <1210639184.3661.43.camel@localhost.localdomain> <20080513145449.GC20806@duck.suse.cz> <1210717389.3638.24.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Badari Pulavarty , akpm@linux-foundation.org, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org To: Mingming Cao Return-path: Received: from styx.suse.cz ([82.119.242.94]:42426 "EHLO mail.suse.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752226AbYENRI7 (ORCPT ); Wed, 14 May 2008 13:08:59 -0400 Content-Disposition: inline In-Reply-To: <1210717389.3638.24.camel@localhost.localdomain> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue 13-05-08 15:23:09, Mingming Cao wrote: > On Tue, 2008-05-13 at 16:54 +0200, Jan Kara wrote: > > On Mon 12-05-08 17:39:43, Mingming Cao wrote: > > > On Mon, 2008-05-12 at 17:54 +0200, Jan Kara wrote: > > > Does this match what you are thinking? It certainly slow down the DIO > > > path, but the positive side is it doesn't disturb the other code path... > > > thanks for your feedback! > > > > > > -------------------------------------------- > > > > > > An unexpected EIO error gets returned when writing to a file > > > using buffered writes and DIO writes at the same time. > > > > > > We found there are a number of places where journal_try_to_free_buffers() > > > could race with journal_commit_transaction(), the later still > > > helds the reference to the buffers on the t_syncdata_list or t_locked_list > > > , while journal_try_to_free_buffers() tries to free them, which resulting an EIO > > > error returns back to the dio caller. > > > > > > The logic fix is to retry freeing if journal_try_to_free_buffers() to failed > > > to free those data buffers while journal_commit_transaction() is still > > > reference those buffers. > > > This is done via implement ext3 launder_page() callback, instead of inside > > > journal_try_to_free_buffers() itself, so that it doesn't affecting other code > > > path calling journal_try_to_free_buffers and only dio path get affected. > > > > > > Signed-off-by: Mingming Cao > > > Index: linux-2.6.26-rc1/fs/ext3/inode.c > > > =================================================================== > > > --- linux-2.6.26-rc1.orig/fs/ext3/inode.c 2008-05-03 11:59:44.000000000 -0700 > > > +++ linux-2.6.26-rc1/fs/ext3/inode.c 2008-05-12 12:41:27.000000000 -0700 > > > @@ -1766,6 +1766,23 @@ static int ext3_journalled_set_page_dirt > > > return __set_page_dirty_nobuffers(page); > > > } > > > > > > +static int ext3_launder_page(struct page *page) > > > +{ > > > + int ret; > > > + int retry = 5; > > > + > > > + while (retry --) { > > > + ret = ext3_releasepage(page, GFP_KERNEL); > > > + if (ret == 1) > > > + break; > > > + else > > > + schedule(); > > > + } > > > + > > > + return ret; > > > +} > > > + > > > + > > Yes, I meant something like this. We could be more clever and do: > > > > head = bh = page_buffers(page); > > do { > > wait_on_buffer(bh); > > bh = bh->b_this_page; > > } while (bh != head); > > /* > > * Now commit code should have been able to proceed and release > > * those buffers > > */ > > schedule(); > > > > Bummer, we can't free buffers in ext3_launder_page() before calling > try_to_free_page, as later > invalidate_complete_page2()->try_to_free_page() expecting the page > buffers are still here, and will return EIO if it launder_page() has > already freed those buffers.:( Are you sure? Because if bufferes are released in ext3_launder_page(), PagePrivate() has been set to 0 and we should directly fall through to releasing the page without ever calling try_to_release_page()... So I'd want to find out why PagePrivate is still set in invalidate_complete_page2(). > Doing wait_on_buffer() alone in launder_page() is not enough as it > doesn't wait for buffer reference drop to 0. Yes, this would not be enough. Honza -- Jan Kara SUSE Labs, CR