From: Hisashi Hifumi Subject: Re: [PATCH] jbd jbd2: fix dio write returning EIO whentry_to_release_page fails Date: Tue, 05 Aug 2008 11:36:15 +0900 Message-ID: <6.0.0.20.2.20080805104519.03c9b3d8@172.19.0.2> References: <6.0.0.20.2.20080804185338.03bcd488@172.19.0.2> <20080804145047.04794bf3.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: cmm@us.ibm.com, jack@suse.cz, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Andrew Morton Return-path: Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:60491 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754101AbYHECiP (ORCPT ); Mon, 4 Aug 2008 22:38:15 -0400 In-Reply-To: <20080804145047.04794bf3.akpm@linux-foundation.org> References: <6.0.0.20.2.20080804185338.03bcd488@172.19.0.2> <20080804145047.04794bf3.akpm@linux-foundation.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: >> >> diff -Nrup linux-2.6.27-rc1.org/fs/jbd/transaction.c >linux-2.6.27-rc1/fs/jbd/transaction.c >> --- linux-2.6.27-rc1.org/fs/jbd/transaction.c 2008-07-29 >19:28:47.000000000 +0900 >> +++ linux-2.6.27-rc1/fs/jbd/transaction.c 2008-07-29 20:40:12.000000000 +0900 >> @@ -1764,6 +1764,12 @@ int journal_try_to_free_buffers(journal_ >> */ >> if (ret == 0 && (gfp_mask & __GFP_WAIT) && (gfp_mask & __GFP_FS)) { >> journal_wait_for_transaction_sync_data(journal); >> + >> + bh = head; >> + do { >> + while (atomic_read(&bh->b_count)) >> + schedule(); >> + } while ((bh = bh->b_this_page) != head); >> ret = try_to_free_buffers(page); >> } > >The loop is problematic. If the scheduler decides to keep running this >task then we have a busy loop. If this task has realtime policy then >it might even lock up the kernel. > >Perhaps we can use wait_on_page_writeback()? > We cannot use wait_on_page_writeback() to wait for releasing bh ref because in ext3_ordered_writepage() bh ref is grabbed and released through walk_page_buffers so between both walk_page_buffers, it remains taking a bh ref even if end_page_writeback is performed. ->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): ---> remains taking a bh ref walk_page_buffers() <-release a bh ref