From: Prarit Bhargava <prarit@redhat•com>
To: Jessica Yu <jeyu@kernel•org>, Heiko Carstens <heiko.carstens@de•ibm.com>
Cc: linux-next@vger•kernel.org, linux-kernel@vger•kernel.org,
linux-s390@vger•kernel.org, Cathy Avery <cavery@redhat•com>
Subject: Re: [-next] system hangs likely due to "modules: Only return -EEXIST for modules that have finished loading"
Date: Fri, 26 Apr 2019 14:10:15 -0400 [thread overview]
Message-ID: <2e047a7e-bf08-be8c-bdd0-429464fa133d@redhat.com> (raw)
In-Reply-To: <20190426160956.GA3827@linux-8ccs>
On 4/26/19 12:09 PM, Jessica Yu wrote:
> +++ Heiko Carstens [26/04/19 17:07 +0200]:
>> On Fri, Apr 26, 2019 at 09:22:34AM -0400, Prarit Bhargava wrote:
>>> On 4/26/19 9:07 AM, Heiko Carstens wrote:
>>> > Hello Prarit,
>>> >
>>> > it looks like your commit f9a75c1d717f ("modules: Only return -EEXIST
>>> > for modules that have finished loading") _sometimes_ causes hangs on
>>> > s390. This is unfortunately not 100% reproducible, however the
>>> > mentioned commit seems to be the only relevant one in modules.c.
>>> >
>>> > What I see is a hanging system with messages like this on the console:
>>> >
>>> > [ 65.876040] rcu: INFO: rcu_sched self-detected stall on CPU
>>> > [ 65.876049] rcu: 7-....: (5999 ticks this GP)
>>> idle=eae/1/0x4000000000000002 softirq=1181/1181 fqs=2729
>>> > [ 65.876078] (t=6000 jiffies g=-471 q=17196)
>>> > [ 65.876084] Task dump for CPU 7:
>>> > [ 65.876088] systemd-udevd R running task 0 731 721
>>> 0x06000004
>>> > [ 65.876097] Call Trace:
>>> > [ 65.876113] ([<0000000000abb264>] __schedule+0x2e4/0x6e0)
>>> > [ 65.876122] [<00000000001ee486>] finished_loading+0x4e/0xb0
>>> > [ 65.876128] [<00000000001f1ed6>] load_module+0xcce/0x27a0
>>> > [ 65.876134] [<00000000001f3af0>] __s390x_sys_init_module+0x148/0x178
>>> > [ 65.876142] [<0000000000ac0766>] system_call+0x2aa/0x2c8
>>> > I did not look any further into the dump, however since the commit
>>> > touches exactly the code path which seems to be looping... ;)
>>> >
>>>
>>> Ouch :( I wonder if I exposed a further race or another bug. Heiko, can you
>>> determine which module is stuck? Warning: I have not compiled this code.
>>
>> Here we go:
>>
>> [ 11.716866] PRARIT: waiting for module s390_trng to load.
>> [ 11.716867] PRARIT: waiting for module s390_trng to load.
>> [ 11.716868] PRARIT: waiting for module s390_trng to load.
>> [ 11.716870] PRARIT: waiting for module s390_trng to load.
>> [ 11.716871] PRARIT: waiting for module s390_trng to load.
>> [ 11.716872] PRARIT: waiting for module s390_trng to load.
>> [ 11.716874] PRARIT: waiting for module s390_trng to load.
>> [ 11.716875] PRARIT: waiting for module s390_trng to load.
>> [ 11.716876] PRARIT: waiting for module s390_trng to load.
>> [ 16.726850] add_unformed_module: 31403529 callbacks suppressed
>> [ 16.726853] PRARIT: waiting for module s390_trng to load.
>> [ 16.726862] PRARIT: waiting for module s390_trng to load.
>> [ 16.726865] PRARIT: waiting for module s390_trng to load.
>> [ 16.726867] PRARIT: waiting for module s390_trng to load.
>> [ 16.726869] PRARIT: waiting for module s390_trng to load.
>>
>> If I'm not mistaken then there was _no_ corresponding message on the
>> console stating that the module already exists.
Heiko,
Where is the s390_trng module? I can't seem to find it in the tree.
[02:06 PM root@ibm-z-108 linux-next]# find ./ -name *s390_trng*
[02:06 PM root@ibm-z-108 linux-next]# git grep s390_trng
[02:07 PM root@ibm-z-108 linux-next]#
P.
>
> Hm, my current theory is that we have a module whose exit() function
> is taking a while to run to completion. While it is doing so, the
> module's state is already set to MODULE_STATE_GOING.
>
> With Prarit's patch, since this module is probably still in GOING,
> add_unformed_module() will wait until the module is finally gone. If
> this takes too long, we will keep trying to add ourselves to the
> module list and hence stay in the loop in add_unformed_module().
> According to Documentation/RCU/stallwarn.txt, this looping in the
> kernel may trigger an rcu stall warning (see bullet point stating "a
> CPU looping anywhere in the kernel without invoking schedule()".
>
> Heiko, could you modify the patch to print the module's state to
> confirm?
>
> Thanks,
>
> Jessica
next prev parent reply other threads:[~2019-04-26 18:10 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-26 13:07 [-next] system hangs likely due to "modules: Only return -EEXIST for modules that have finished loading" Heiko Carstens
2019-04-26 13:22 ` Prarit Bhargava
2019-04-26 15:07 ` Heiko Carstens
2019-04-26 16:09 ` Jessica Yu
2019-04-26 17:15 ` Prarit Bhargava
2019-04-26 18:10 ` Prarit Bhargava [this message]
2019-04-26 19:45 ` Prarit Bhargava
2019-04-27 0:20 ` Prarit Bhargava
2019-04-27 10:24 ` Heiko Carstens
2019-04-27 10:35 ` Prarit Bhargava
2019-04-27 10:42 ` Prarit Bhargava
2019-04-29 5:55 ` Heiko Carstens
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