On Wed, Apr 04, 2012 at 09:55:20AM +0200, Jan Kara wrote: > On Tue 10-01-12 13:12:55, Josef Bacik wrote: > > If we are journalling data (ie journal=data or big symlinks) we can discard > > buffers and move them to different transactions to make sure they get cleaned up > > properly. The problem is b_modified could still be set from the last > > transaction that touched it, so putting it on the currently running transaction > > or setting it up to be put on the next transaction will run into problems if the > > buffer gets reused in that transaction as the space accounting logic won't be > > done, which will result in panics at commit time because t_nr_buffers will end > > up being more than t_outstanding_credits. Thanks to Jan Kara for pointing out > > the other part of this problem a few months ago. Thanks, > > > > Signed-off-by: Josef Bacik <josef@xxxxxxxxxx> > So I think I've nailed this down. Your feeling that the problem is with > refiling buffer to BJ_Forget list of the running transaction was right. The > missing piece to the puzzle was that journal_invalidatepage() can get > called not only when underlying block is freed but also when someone > flushes page cache. The traces I have suggest that someone has flushed page > cache (likely of the block device), that moved buffer from the checkpoint > list to BJ_Forget list of the running transaction and then the same running > transaction tried to modify the buffer which triggered the accounting > problem you spotted. > > I have updated the changelog and pushed the patch to my tree (for JBD > only). I'll duplicate the patch for JBD2 tomorrow. > Ok now it's my turn to be unsure ;). I thought invalidatepage could only be called via truncate? You say it happens when someone flushes pagecache, do you mean like echo 3 > /proc/sys/vm/drop_caches? I've followed invalidatepage and can't see what you are talking about, so as usual I need it explained to me because I'm stupid. Thanks, Josef -- 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
