Re: task btrfs-cleaner:770 blocked for more than 120 seconds.

[Roman Mamedov <rm@romanrm.net>]

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On Sun, 14 Feb 2016 13:32:24 -0800
Liu Bo <bo.li.liu@oracle.com> wrote:

> Hi Mike,
> On Sun, Feb 14, 2016 at 12:23:16AM +0500, Михаил Гаврилов wrote:
> > Sorry, I have not yet had time to apply your patch.
> > 
> > And get hang again when launch web browser.
> > 
> > Here new logs: http://btrfs.sy24.ru/kernel-sysrqw-btrfscleaner770blocked-3.txt
> 
> The logs show,
> every hung process is waiting for fs tree root's WRITE_LOCK, but someone who's
> holding the WRITE_LOCK is not reflected here.
> 
> Only one suspicious process is 
> "Chrome_FileThre D ffff8807fe1d7a18 10360 22486   2826 0x00000000"
> it's also waiting on btrfs_tree_lock(), but I can't tell whether it
> waits for the fs tree root node's lock or the children node's lock.
> 
> Hmm, sorry for not being helpful, but I was wondering if this also
> occurs on the latest btrfs(4.5) or is it possible to give it a shot?
> 
> The best result is that it's been fixed by one commit in 4.5.

FWIW I had a persistently repeating deadlock on 4.1 and 4.3, but after upgrade
to 4.4 it no longer happens. Not sure if it might be related or not, the
backtrace seems similar: http://www.spinics.net/lists/linux-btrfs/msg50951.html

My advice would be to try 4.4, but don't forget to manually add the
nocow/enospc patch: https://patchwork.kernel.org/patch/7967161/

None of the vanilla 4.1, 4.3 or 4.4 should be considered usable with Btrfs at
the moment. The latest kernel series which works out of the box was 3.18;
patched 4.4 also works fine so far, but I wonder if that patch makes it into
4.4.2 or gets forgotten/etc again.

-- 
With respect,
Roman

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