From: Adrian Bunk Subject: [RFC: 2.6.16 patch] jbd: journal_dirty_data re-check for unmapped buffers Date: Wed, 4 Apr 2007 05:41:42 +0200 Message-ID: <20070404034142.GA27660@stusta.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: linux-ext4@vger.kernel.org To: Eric Sandeen Return-path: Received: from mailout.stusta.mhn.de ([141.84.69.5]:42186 "EHLO mailhub.stusta.mhn.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1030380AbXDDDlo (ORCPT ); Tue, 3 Apr 2007 23:41:44 -0400 Content-Disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org This patch also seems to make sense for 2.6.16, or do I miss anything? TIA Adrian commit f58a74dca88d48b0669609b4957f3dd757bdc898 Author: Eric Sandeen Date: Sat Oct 28 10:38:27 2006 -0700 [PATCH] jbd: journal_dirty_data re-check for unmapped buffers When running several fsx's and other filesystem stress tests, we found cases where an unmapped buffer was still being sent to submit_bh by the ext3 dirty data journaling code. I saw this happen in two ways, both related to another thread doing a truncate which would unmap the buffer in question. Either we would get into journal_dirty_data with a bh which was already unmapped (although journal_dirty_data_fn had checked for this earlier, the state was not locked at that point), or it would get unmapped in the middle of journal_dirty_data when we dropped locks to call sync_dirty_buffer. By re-checking for mapped state after we've acquired the bh state lock, we should avoid these races. If we find a buffer which is no longer mapped, we essentially ignore it, because journal_unmap_buffer has already decided that this buffer can go away. I've also added tracepoints in these two cases, and made a couple other tracepoint changes that I found useful in debugging this. Signed-off-by: Eric Sandeen Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c index d5c6304..4f82bcd 100644 --- a/fs/jbd/transaction.c +++ b/fs/jbd/transaction.c @@ -967,6 +967,13 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh) */ jbd_lock_bh_state(bh); spin_lock(&journal->j_list_lock); + + /* Now that we have bh_state locked, are we really still mapped? */ + if (!buffer_mapped(bh)) { + JBUFFER_TRACE(jh, "unmapped buffer, bailing out"); + goto no_journal; + } + if (jh->b_transaction) { JBUFFER_TRACE(jh, "has transaction"); if (jh->b_transaction != handle->h_transaction) { @@ -1028,6 +1035,11 @@ int journal_dirty_data(handle_t *handle, struct buffer_head *bh) sync_dirty_buffer(bh); jbd_lock_bh_state(bh); spin_lock(&journal->j_list_lock); + /* Since we dropped the lock... */ + if (!buffer_mapped(bh)) { + JBUFFER_TRACE(jh, "buffer got unmapped"); + goto no_journal; + } /* The buffer may become locked again at any time if it is redirtied */ } @@ -1824,6 +1836,7 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh) } } } else if (transaction == journal->j_committing_transaction) { + JBUFFER_TRACE(jh, "on committing transaction"); if (jh->b_jlist == BJ_Locked) { /* * The buffer is on the committing transaction's locked @@ -1838,7 +1851,6 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh) * can remove it's next_transaction pointer from the * running transaction if that is set, but nothing * else. */ - JBUFFER_TRACE(jh, "on committing transaction"); set_buffer_freed(bh); if (jh->b_next_transaction) { J_ASSERT(jh->b_next_transaction == @@ -1858,6 +1870,7 @@ static int journal_unmap_buffer(journal_t *journal, struct buffer_head *bh) * i_size already for this truncate so recovery will not * expose the disk blocks we are discarding here.) */ J_ASSERT_JH(jh, transaction == journal->j_running_transaction); + JBUFFER_TRACE(jh, "on running transaction"); may_free = __dispose_buffer(jh, transaction); }