On 03/14/2014 09:13 AM, Wang Shilong wrote: >> Lets try this again. We can deadlock the box if we send on a box and try to >> write onto the same fs with the app that is trying to listen to the send >> pipe. >> This is because the writer could get stuck waiting for a transaction commit >> which is being blocked by the send. So fix this by making sure looking at >> the >> commit roots is always going to be consistent. We do this by keeping track >> of >> which roots need to have their commit roots swapped during commit, and then >> taking the commit_root_sem and swapping them all at once. Then make sure we >> take a read lock on the commit_root_sem in cases where we search the commit >> root >> to make sure we're always looking at a consistent view of the commit roots. >> Previously we had problems with this because we would swap a fs tree commit >> root >> and then swap the extent tree commit root independently which would cause the >> backref walking code to screw up sometimes. With this patch we no longer >> deadlock and pass all the weird send/receive corner cases. Thanks, > > Now btrfs send are alway searching commit root! Your codes only seems to > protect backref codes, > it reduce transaction blocked but make it not safe as we have discussed > before. > >
I was trying to remember why we didn't like this solution before but I couldn't come up with anything. Apparently I haven't completely fixed the problem yet so stay tuned for what I do next ;). Thanks, Josef -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
