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.
