Date: Mon, 23 Oct 2006 15:40:48 -0500 From: Eric Sandeen Subject: [PATCH RHEL5] handle races w/ truncate in journal_dirty_data() This is for BZ 209647 : ext3/jbd panic This patch is now in -mm. 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 --- fs/jbd/transaction.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) Index: linux-2.6.18-1.2732.el5/fs/jbd/transaction.c =================================================================== --- linux-2.6.18-1.2732.el5.orig/fs/jbd/transaction.c +++ linux-2.6.18-1.2732.el5/fs/jbd/transaction.c @@ -967,6 +967,13 @@ int journal_dirty_data(handle_t *handle, */ 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, 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 */ } @@ -1823,6 +1835,7 @@ static int journal_unmap_buffer(journal_ } } } 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 @@ -1837,7 +1850,6 @@ static int journal_unmap_buffer(journal_ * 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 == @@ -1857,6 +1869,7 @@ static int journal_unmap_buffer(journal_ * 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); }
