From: Hisashi Hifumi Subject: Re: [PATCH] jbd jbd2: fixdiowritereturningEIOwhentry_to_release_page fails Date: Thu, 21 Aug 2008 16:47:05 +0900 Message-ID: <6.0.0.20.2.20080821164123.04015400@172.19.0.2> References: <1217971027.7516.20.camel@mingming-laptop> <1218029114.15342.58.camel@think.oraclecorp.com> <20080806135337.GA3615@duck.suse.cz> <1218063477.6383.41.camel@mingming-laptop> <6.0.0.20.2.20080807115853.03f95b78@172.19.0.2> <1218104494.15342.171.camel@think.oraclecorp.com> <6.0.0.20.2.20080808113605.04141328@172.19.0.2> <1218200055.15342.230.camel@think.oraclecorp.com> <6.0.0.20.2.20080811123405.03ec03d0@172.19.0.2> <1218547706.15342.305.camel@think.oraclecorp.com> <20080813101650.GA14392@duck.suse.cz> <1218632396.15342.340.camel@think.oraclecorp.com> <6.0.0.20.2.20080819113242.03f9e8c8@172.19.0.2> <20080819001651.30c7620f.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Chris Mason , Jan Kara , MingmingCao , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, Zach Brown To: Andrew Morton Return-path: Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:59766 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752155AbYHUHtZ (ORCPT ); Thu, 21 Aug 2008 03:49:25 -0400 In-Reply-To: <20080819001651.30c7620f.akpm@linux-foundation.org> References: <1217971027.7516.20.camel@mingming-laptop> <1218029114.15342.58.camel@think.oraclecorp.com> <20080806135337.GA3615@duck.suse.cz> <1218063477.6383.41.camel@mingming-laptop> <6.0.0.20.2.20080807115853.03f95b78@172.19.0.2> <1218104494.15342.171.camel@think.oraclecorp.com> <6.0.0.20.2.20080808113605.04141328@172.19.0.2> <1218200055.15342.230.camel@think.oraclecorp.com> <6.0.0.20.2.20080811123405.03ec03d0@172.19.0.2> <1218547706.15342.305.camel@think.oraclecorp.com> <20080813101650.GA14392@duck.suse.cz> <1218632396.15342.340.camel@think.oraclecorp.com> <6.0.0.20.2.20080819113242.03f9e8c8@172.19.0.2> <20080819001651.30c7620f.akpm@linux-foundation.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: At 16:16 08/08/19, Andrew Morton wrote: >On Tue, 19 Aug 2008 16:03:45 +0900 Hisashi Hifumi > wrote: > >> >> At 21:59 08/08/13, Chris Mason wrote: >> >On Wed, 2008-08-13 at 12:16 +0200, Jan Kara wrote: >> > >> >> > With that said, I don't have strong feelings against falling back to >> >> > buffered IO when the invalidate fails. Maybe Zach remembers something I >> >> > don't? >> >> I don't have a strong opinion either. Falling back to buffered writes is >> >> simpler at least for ext3/ext4 because properly synchronizing against >> >> writepage() call does not seem to have a nice solution either in >> >> do_launder_page() or in releasepage(). OTOH is hides the fact the invalidate >> >> is failing and so if we screw up something in future and it fails often, it >> >> might be hard to notice / track down the performance penalty. >> > >> >In general, these races don't happen often, and when they do it is >> >because someone is mixing page cache and O_DIRECT io to the same file. >> >That is explicitly outside the main use case of O_DIRECT. >> > >> >So, I'd rather see us slow down O_DIRECT in the mixed use case than have >> >big impacts in complexity or speed to other parts of the kernel. If >> >falling back avoids problems in some filesystems or avoids clearing the >> >uptodate bit unexpectedly, I'd much rather take the fallback patch. >> > >> >-chris >> >> Hi Andrew. >> I think we don't have strong feelings against falling back to buffered >writes to >> fix the direct-io -EIO problem. >> >> Please review my patch. >> > >umm, what problem does it solve? > >If I recall correctly, we had a problem with pages which are pinned by >an ext3 transaction, and those pages weren't releaseable for direct-io, >and this caused some problem? Hi Andrew. Sorry, I should describe about this problem. Yes, Dio write returns EIO when try_to_release_page fails because sometimes bh is still referenced by jbd or other place. The race between freeing buffer and committing transaction(jbd) was fixed but I found another race. We have been discussing about this issue, and I proposed that falling back to buffered writes to fix this issue. I think we don't have strong feelings against falling back to buffered writes to fix the direct-io -EIO problem. > >I think falling back to buffered writes is always a safe course, but >it'd be nice to have a full description of the change, please. [PATCH] VFS: fix dio write returning EIO when try_to_release_page fails Dio write returns EIO when try_to_release_page fails because bh is still referenced. The patch "commit 3f31fddfa26b7594b44ff2b34f9a04ba409e0f91 Author: Mingming Cao Date: Fri Jul 25 01:46:22 2008 -0700 jbd: fix race between free buffer and commit transaction " was merged into 2.6.27-rc1, but I noticed that this patch is not enough to fix the race. I did fsstress test heavily to 2.6.27-rc1, and found that dio write still sometimes got EIO through this test. The patch above fixed race between freeing buffer(dio) and committing transaction(jbd) but I discovered that there is another race, freeing buffer(dio) and ext3/4_ordered_writepage. : background_writeout() ->write_cache_pages() ->ext3_ordered_writepage() walk_page_buffers() -> take a bh ref block_write_full_page() -> unlock_page : <- end_page_writeback : <- race! (dio write->try_to_release_page fails) walk_page_buffers() ->release a bh ref ext3_ordered_writepage holds bh ref and does unlock_page remaining taking a bh ref, so this causes the race and failure of try_to_release_page. To fix this race, I used the approach of falling back to buffered writes if try_to_release_page fails on a page. Signed-off-by: Hisashi Hifumi diff -Nrup linux-2.6.27-rc3.org/mm/filemap.c linux-2.6.27-rc3/mm/filemap.c --- linux-2.6.27-rc3.org/mm/filemap.c 2008-08-13 13:48:47.000000000 +0900 +++ linux-2.6.27-rc3/mm/filemap.c 2008-08-19 15:45:31.000000000 +0900 @@ -2129,13 +2129,20 @@ generic_file_direct_write(struct kiocb * * After a write we want buffered reads to be sure to go to disk to get * the new data. We invalidate clean cached page from the region we're * about to write. We do this *before* the write so that we can return - * -EIO without clobbering -EIOCBQUEUED from ->direct_IO(). + * without clobbering -EIOCBQUEUED from ->direct_IO(). */ if (mapping->nrpages) { written = invalidate_inode_pages2_range(mapping, pos >> PAGE_CACHE_SHIFT, end); - if (written) + /* + * If a page can not be invalidated, return 0 to fall back + * to buffered write. + */ + if (written) { + if (written == -EBUSY) + return 0; goto out; + } } written = mapping->a_ops->direct_IO(WRITE, iocb, iov, pos, *nr_segs); diff -Nrup linux-2.6.27-rc3.org/mm/truncate.c linux-2.6.27-rc3/mm/truncate.c --- linux-2.6.27-rc3.org/mm/truncate.c 2008-08-13 13:48:48.000000000 +0900 +++ linux-2.6.27-rc3/mm/truncate.c 2008-08-19 12:10:46.000000000 +0900 @@ -380,7 +380,7 @@ static int do_launder_page(struct addres * Any pages which are found to be mapped into pagetables are unmapped prior to * invalidation. * - * Returns -EIO if any pages could not be invalidated. + * Returns -EBUSY if any pages could not be invalidated. */ int invalidate_inode_pages2_range(struct address_space *mapping, pgoff_t start, pgoff_t end) @@ -440,7 +440,7 @@ int invalidate_inode_pages2_range(struct ret2 = do_launder_page(mapping, page); if (ret2 == 0) { if (!invalidate_complete_page2(mapping, page)) - ret2 = -EIO; + ret2 = -EBUSY; } if (ret2 < 0) ret = ret2;