On Thu 05-05-11 08:49:14, Eric Sandeen wrote: > On 5/5/11 7:10 AM, Jan Kara wrote: > > In do_get_write_access() we wait on BH_Unshadow bit for buffer to get > > from shadow state. The waking code in journal_commit_transaction() has > > a bug because it does not issue a memory barrier after the buffer is moved > > from the shadow state and before wake_up_bit() is called. Thus a waitqueue > > check can happen before the buffer is actually moved from the shadow state > > and waiting process may never be woken. Fix the problem by issuing proper > > barrier. > > needed for jbd/commit.c as well, I guess? Yes, I was already queued in my tree. I just sent it to the list as well. Honza > > diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c > > index 2e5d370..3a958c7 100644 > > --- a/fs/jbd2/commit.c > > +++ b/fs/jbd2/commit.c > > @@ -768,8 +768,13 @@ wait_for_iobuf: > > required. */ > > JBUFFER_TRACE(jh, "file as BJ_Forget"); > > jbd2_journal_file_buffer(jh, commit_transaction, BJ_Forget); > > - /* Wake up any transactions which were waiting for this > > - IO to complete */ > > + /* > > + * Wake up any transactions which were waiting for this IO to > > + * complete. The barrier must be here so that changes by > > + * jbd2_journal_file_buffer() take effect before wake_up_bit() > > + * does the waitqueue check. > > + */ > > + smp_mb(); > > wake_up_bit(&bh->b_state, BH_Unshadow); > > JBUFFER_TRACE(jh, "brelse shadowed buffer"); > > __brelse(bh); > -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
