Bug#638467: linux-image-3.0.0: btrfs causes bittorrent clients to hang

[Moritz Muehlenhoff <jmm@inutil.org>]

reassign 638467 src:linux
severity 638467 normal
tags 638467 moreinfo
thanks

On Fri, Aug 19, 2011 at 08:08:33AM -0600, Matthew wrote:
> Package: linux-image-3.0.0
> Version: linux-image-3.0.0-1-686-pae
> Severity: important
> 
> 
> This computer has been quite stable for several years. It often runs azureus/vuze for weeks at a time. It has 5.5T of disk which I swithced to btrfs, and I've been quite happy with btrfs since kernel version 2.28. I recently upgraded to kernel version 3.0.0 because it was supposed to have some brfs fixes. I soon noticed that vuze would hang, showing 100% CPU usage, after running for a few hours. 
> 
> I have now been able to reproduce this problem with both azureus/vuze and deluge. If I start downloading some torrents right after a reboot, things work, at first. Then the btrfs processes start taking more and more CPU time. Iostat shows a very high number of writes per second, but a tiny amount of actual data written, and a "utilization" of 100% on several disks.  This disk activity start to make the bittorrent client hang, so that downloading at full speed happens for shorter and shorter periods, while it spends more and more time waiting for I/O. Eventually it gets to the point that the bittorrent client is downloading nothing at all, but shows 100% CPU utilization in top. For both azureus and deluge, when the program shows 100% CPU, killing it only creates a zombie that continues to take 100% CPU until I reboot the machine. Oh, and when the azureus or deluge program hangs at 100% CPU, the cpu usage for the btrfs processes, and the writes reported by iostat, drop to zero.
> 
> Last night I reverted to kernel  linux-image-2.6.38-2-686, which has completely fixed the problem.
> 
> I've been really impressed with btrfs, and hope I can do somthing to help with this problem. Please feel free to contact me if there's any more information I can provide. 

Has this been fixed in more recent kernels, e.g. the Wheezy kernel?

Cheers,
        Moritz