Not sure if the stack is crap or not, but this looks like an RCU crash?
https://i.imgur.com/sBnNe1p.jpg
Kyle.
FileServer ~ # uname -a
Linux FileServer.OpenWRT.local 4.12.5-gentoo #1 SMP PREEMPT Fri Aug 18
17:23:00 PDT 2017 x86_64 Intel(R) Atom(TM) CPU 330 @ 1.60GHz
GenuineIntel GNU/Linux
FileServer ~ # cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 28
model name : Intel(R) Atom(TM) CPU 330 @ 1.60GHz
stepping : 2
microcode : 0x20d
cpu MHz : 1999.917
cache size : 512 KB
physical id : 0
siblings : 4
core id : 0
cpu cores : 2
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de tsc msr pae mce cx8 apic sep mtrr pge mca
cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm
constant_tsc arch_perfmon pebs bts nopl cpuid aperfmperf pni dtes64
monitor ds_cpl tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm dtherm
bugs :
bogomips : 3999.83
clflush size : 64
cache_alignment : 64
address sizes : 32 bits physical, 48 bits virtual
power management:
On Thu, Sep 28, 2017 at 8:32 PM, Kyle Sanderson <[email protected]> wrote:
> Not sure if the stack is crap or not, but this looks like an RCU crash?
>
> https://i.imgur.com/sBnNe1p.jpg
Hmm. Not the clearest picture, and the "Code:" line in particular is
missing the interesting part, but at a guess it's taking a fault in
put_cred(), which inlines to
if (atomic_dec_and_test(&(cred)->usage))
__put_cred(cred);
and I think it's that "cred" pointer that may be NULL, which makes
"&(cred)->usage" be a NULL pointer too, and you get a page fault when
it tries to decrement the usage count.
Now, it goes without saying that the cred pointer should never *be*
NULL on a filp that is on the RCU freeing list, because we always
initialize file->f_cred when we allocate a file to the current creds.
So there's something odd going on. Possibly entirely unrelated memory
corruption.
Nothing obvious stands out, I think we'd need to see more of a pattern
of the problem to see what is up.
Linus
On Thu, Sep 28, 2017 at 09:00:52PM -0700, Linus Torvalds wrote:
> On Thu, Sep 28, 2017 at 8:32 PM, Kyle Sanderson <[email protected]> wrote:
> > Not sure if the stack is crap or not, but this looks like an RCU crash?
> >
> > https://i.imgur.com/sBnNe1p.jpg
>
> Hmm. Not the clearest picture, and the "Code:" line in particular is
> missing the interesting part, but at a guess it's taking a fault in
> put_cred(), which inlines to
>
> if (atomic_dec_and_test(&(cred)->usage))
> __put_cred(cred);
>
> and I think it's that "cred" pointer that may be NULL, which makes
> "&(cred)->usage" be a NULL pointer too, and you get a page fault when
> it tries to decrement the usage count.
>
> Now, it goes without saying that the cred pointer should never *be*
> NULL on a filp that is on the RCU freeing list, because we always
> initialize file->f_cred when we allocate a file to the current creds.
>
> So there's something odd going on. Possibly entirely unrelated memory
> corruption.
>
> Nothing obvious stands out, I think we'd need to see more of a pattern
> of the problem to see what is up.
Kyle, if this is reproducible, please build your kernel with
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. This can detect the call_rcu()
equivalent of a double free, and these double frees have sometimes
resulted in output looking something like the .jpg along with the
NULL-pointer problem that Linus suspects.
Thanx, Paul
