2006-10-16 18:24:43

by Eric Sandeen

[permalink] [raw]
Subject: [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

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 <[email protected]>

Index: linux-2.6.18/fs/jbd/transaction.c
--- linux-2.6.18.orig/fs/jbd/transaction.c
+++ linux-2.6.18/fs/jbd/transaction.c
@@ -967,6 +967,13 @@ int journal_dirty_data(handle_t *handle,
+ /* 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,
+ /* 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");
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);