2006-10-28 17:38:44

by Andrew Morton

[permalink] [raw]
Subject: [patch 06/38] jbd2: journal_dirty_data re-check for unmapped buffers

From: Eric Sandeen <[email protected]>

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 <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

fs/jbd2/transaction.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)

diff -puN fs/jbd2/transaction.c~jbd2-journal_dirty_data-re-check-for-unmapped-buffers fs/jbd2/transaction.c
--- a/fs/jbd2/transaction.c~jbd2-journal_dirty_data-re-check-for-unmapped-buffers
+++ a/fs/jbd2/transaction.c
@@ -967,6 +967,13 @@ int jbd2_journal_dirty_data(handle_t *ha
+ /* 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 jbd2_journal_dirty_data(handle_t *ha
+ /* 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_
} 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_
* 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 ==
@@ -1858,6 +1870,7 @@ 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);