Re: [GIT PULL] Btrfs deadlock fix

[Chris Mason <clm@fb.com>]

On Sun, Nov 23, 2014 at 7:23 PM, Benjamin Herrenschmidt 
<benh@kernel.crashing.org> wrote:
> On Sun, 2014-11-23 at 10:14 -0500, Chris Mason wrote:
>>  Hi Linus,
>> 
>>  My for-linus branch:
> 
> Not sure if this is related, but with -rc4, on this ppc64el box, when
> grub updates (it starts trying to mount everything under the sun with
> every filesystem), the box hangs with:
> 
> [  177.344522] INFO: rcu_sched detected stalls on CPUs/tasks: { 8}
> (detected by 9, t=25883 jiffies, g=3642, c=3641, q=5206)
> 
> With xmon I can catch it with this backtrace:
> 
> [link register   ] d00000000ecec3f8 test_check_exists+0x1f8/0x280 
> [btrfs]
> [c000000f0cc63930] d00000000ecec2b0 test_check_exists+0xb0/0x280 
> [btrfs] (unreliable)
> [c000000f0cc63990] d00000000ed2a4b4 
> btrfs_test_free_space_cache+0x774/0x1150 [btrfs]
> [c000000f0cc63a20] d00000000ed30f04 init_btrfs_fs+0x11c/0x210 [btrfs]
> [c000000f0cc63a90] c00000000000b4dc do_one_initcall+0x12c/0x280
> [c000000f0cc63b60] c0000000001628b8 load_module+0x2088/0x2970
> [c000000f0cc63d50] c0000000001633d0 SyS_finit_module+0xc0/0x120
> [c000000f0cc63e30] c00000000000927c syscall_exit+0x0/0x7c
> --- Exception: c01 (System Call) at 00003fff88697184
> 
> Note that afaik there isn't any btrfs partition on any disk on that
> machine... well not that I know of :)

This should be from CONFIG_BTRFS_FS_RUN_SANITY_TESTS=y.  I do test with 
this on here, but I'll look it over for ppc related fun.

The deadlock fix from this pull shouldn't be related.  Just to make 
sure I read your email right, this stall isn't new with rc6 is it?

-chris