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Commit f58a74dc authored by Eric Sandeen's avatar Eric Sandeen Committed by Linus Torvalds
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[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: default avatarEric Sandeen <esandeen@redhat.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1939e49a

fs/jbd/transaction.c

+14 −1
Original line number Diff line number Diff line
@@ -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);

	}