Re: [GIT PULL] Btrfs deadlock fix

From: Chris Mason
Date: Sun Nov 23 2014 - 19:27:37 EST

On Sun, Nov 23, 2014 at 7:23 PM, Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> 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?


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