Re: linux uml segfault

[Ritesh Raj Sarraf <rrs@debian.org>]

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On Tue, 2021-03-02 at 17:05 +0000, Anton Ivanov wrote:
> > So the best I can extract for you is to compile the kernel with as
> > much
> > information as possible.
> 
> Can you try using one of the older kernels so we can verify if this
> is indeed a 5.10 thing.
> 

That was the first thing I tried. I tested it with 5.10, 5.9 and 5.4.
All 3 crashed. That's when I knew this one was going to be painful one
to conclude.

The only other input I have is that I have one more user who's reported
to be able to reproduce the issue.

OTOH, I have one more user (other than you) who's not been able to
reproduce the issue.

> I will do a dissect the moment I figure out how to reproduce it. I
> will try to do some more experiments on that tomorrow.


Meanwhile, I enabled some debug info in the kernel. Here's what I have
got so far:

```
(gdb) bt
#0  0x00007f89908dc087 in kill () at ../sysdeps/unix/syscall-
template.S:120
#1  0x00000000604a3514 in uml_abort () at arch/um/os-Linux/util.c:94
#2  0x00000000604a3791 in os_dump_core () at arch/um/os-
Linux/util.c:149
#3  0x000000006048d126 in panic_exit (self=0x2e66d5, unused1=6,
unused2=0x0) at arch/um/kernel/um_arch.c:217
#4  0x00000000604c725a in notifier_call_chain (nl=0x2e66d5, val=0,
v=0x60d82f40 <buf>, nr_to_call=-1, nr_calls=0x0) at
kernel/notifier.c:83
#5  0x00000000604c72f6 in atomic_notifier_call_chain (nh=0x2e66d5,
val=6, v=0x0) at kernel/notifier.c:217
#6  0x0000000060a54607 in panic (fmt=0x60a55225 <printk>
"UH\211\345H\201\354", <incomplete sequence \320>) at
kernel/panic.c:272
#7  0x000000006048cca3 in segv (fi=<incomplete type>, ip=1615717312,
is_user=0, regs=0x60c2ee58 <cpu0_irqstack+11864>) at
arch/um/kernel/trap.c:246
#8  0x000000006048ce64 in segv_handler (sig=3040981, unused_si=0x6,
regs=0x60c2ee58 <cpu0_irqstack+11864>) at arch/um/kernel/trap.c:190
#9  0x00000000604a2556 in sig_handler_common (sig=11, si=0x60c2fbf0
<cpu0_irqstack+15344>, mc=0x60c2fae8 <cpu0_irqstack+15080>) at
arch/um/os-Linux/signal.c:48
#10 0x00000000604a2aa2 in sig_handler (sig=3040981, si=0x6, mc=0x0) at
arch/um/os-Linux/signal.c:81
#11 0x00000000604a265f in hard_handler (sig=3040981, si=0x60c2fbf0
<cpu0_irqstack+15344>, p=0x0) at arch/um/os-Linux/signal.c:180
#12 <signal handler called>
#13 0x00000000604de3c0 in printk_caller_id () at
kernel/printk/printk.c:1924
#14 log_output (text_len=<optimized out>, text=<optimized out>,
dev_info=<optimized out>, lflags=<optimized out>, level=<optimized
out>, facility=<optimized out>) at kernel/printk/printk.c:1932
#15 vprintk_store (facility=1624806843, level=5, dev_info=0x0, fmt=0x35
<error: Cannot access memory at address 0x35>, args=0x1) at
kernel/printk/printk.c:2004
#16 0x00000000604de8b7 in vprintk_emit (facility=1624806843,
level=1622768673, dev_info=0x35, fmt=0x1 <error: Cannot access memory
at address 0x1>, args=0x60b97c22) at kernel/printk/printk.c:2029
#17 0x00000000604debad in vprintk_deferred (fmt=0x1 <error: Cannot
access memory at address 0x1>, args=0x60b97c21) at
kernel/printk/printk.c:3079
#18 0x0000000060a554de in printk_deferred (fmt=0x60d895bb <textbuf+91>
"\n") at kernel/printk/printk.c:3091
#19 0x000000006092680f in _warn_unseeded_randomness
(previous=<optimized out>, caller=<optimized out>, func_name=<optimized
out>) at drivers/char/random.c:1534
#20 _warn_unseeded_randomness (func_name=0x60abf380 <__func__.38>
"get_random_u32", caller=0x608b5f25 <bucket_table_alloc+287>,
previous=0x35) at drivers/char/random.c:1516
#21 0x0000000060927d47 in get_random_u32 () at
drivers/char/random.c:2221
#22 0x00000000608b5f25 in bucket_table_alloc (nbuckets=64, gfp=3264,
ht=<optimized out>) at lib/rhashtable.c:203
#23 0x00000000608b6733 in rhashtable_init (ht=0x60c60e30
<init_ipc_ns+80>, params=0x608b5e06 <bucket_table_alloc>) at
lib/rhashtable.c:1061
#24 0x000000006080f234 in ipc_init_ids (ids=0x60c60de8 <init_ipc_ns+8>)
at ipc/util.c:119
#25 0x0000000060813c6d in sem_init_ns (ns=0x60d895bb <textbuf+91>) at
ipc/sem.c:254
#26 0x0000000060015b5d in sem_init () at ipc/sem.c:268
#27 0x00007f89906d92f7 in ?? () from /lib/x86_64-linux-
gnu/libcom_err.so.2
#28 0x00007f8990ab8fb2 in call_init (l=<optimized out>,
argc=argc@entry=5, argv=argv@entry=0x7ffe3e7a4c98,
env=env@entry=0x7ffe3e7a4cc8) at dl-init.c:72
#29 0x00007f8990ab90b9 in call_init (env=0x7ffe3e7a4cc8,
argv=0x7ffe3e7a4c98, argc=5, l=<optimized out>) at dl-init.c:30
#30 _dl_init (main_map=0x61497ea0, argc=5, argv=0x7ffe3e7a4c98,
env=0x7ffe3e7a4cc8) at dl-init.c:119
#31 0x00007f89909d82bd in __GI__dl_catch_exception
(exception=exception@entry=0x0, operate=operate@entry=0x7f8990abc5a0
<call_dl_init>, args=args@entry=0x7ffe3e7a1e80) at dl-error-
skeleton.c:182
#32 0x00007f8990abd028 in dl_open_worker (a=a@entry=0x7ffe3e7a2020) at
dl-open.c:758
#33 0x00007f89909d8260 in __GI__dl_catch_exception
(exception=exception@entry=0x7ffe3e7a2000,
operate=operate@entry=0x7f8990abcc70 <dl_open_worker>,
args=args@entry=0x7ffe3e7a2020) at dl-error-skeleton.c:208
#34 0x00007f8990abc8ca in _dl_open (file=0x7ffe3e7a22a0
"libnss_nis.so.2", mode=-2147483646, caller_dlopen=0x7f89909bf3a6
<nss_load_library+294>, nsid=-2, argc=5, argv=0x7ffe3e7a2000,
env=0x7ffe3e7a4cc8)
    at dl-open.c:837
#35 0x00007f89909d76dd in do_dlopen (ptr=ptr@entry=0x7ffe3e7a2260) at
dl-libc.c:96
#36 0x00007f89909d8260 in __GI__dl_catch_exception
(exception=exception@entry=0x7ffe3e7a21e0,
operate=operate@entry=0x7f89909d76a0 <do_dlopen>,
args=args@entry=0x7ffe3e7a2260) at dl-error-skeleton.c:208
#37 0x00007f89909d831f in __GI__dl_catch_error
(objname=objname@entry=0x7ffe3e7a2238,
errstring=errstring@entry=0x7ffe3e7a2240,
mallocedp=mallocedp@entry=0x7ffe3e7a2237, 
    operate=operate@entry=0x7f89909d76a0 <do_dlopen>,
args=args@entry=0x7ffe3e7a2260) at dl-error-skeleton.c:227
#38 0x00007f89909d77b7 in dlerror_run
(operate=operate@entry=0x7f89909d76a0 <do_dlopen>,
args=args@entry=0x7ffe3e7a2260) at dl-libc.c:46
#39 0x00007f89909d7846 in __GI___libc_dlopen_mode
(name=name@entry=0x7ffe3e7a22a0 "libnss_nis.so.2", mode=mode@entry=-
2147483646) at dl-libc.c:195
#40 0x00007f89909bf3a6 in nss_load_library (ni=ni@entry=0x61497db0) at
nsswitch.c:359
#41 0x00007f89909bfc39 in __GI___nss_lookup_function (ni=0x61497db0,
fct_name=<optimized out>, fct_name@entry=0x7f899089b020 "setgrent") at
nsswitch.c:467
#42 0x00007f899089554b in init_nss_interface () at nss_compat/compat-
grp.c:83
#43 init_nss_interface () at nss_compat/compat-grp.c:79
#44 0x00007f8990895e35 in _nss_compat_getgrnam_r (name=0x7f8990a2a1e0
"tty", grp=0x7ffe3e7a2910, buffer=0x7ffe3e7a24e0 "", buflen=1024,
errnop=0x7f899089eb00) at nss_compat/compat-grp.c:486
#45 0x00007f8990968b85 in __getgrnam_r (name=name@entry=0x7f8990a2a1e0
"tty", resbuf=resbuf@entry=0x7ffe3e7a2910,
buffer=buffer@entry=0x7ffe3e7a24e0 "", buflen=1024,
result=result@entry=0x7ffe3e7a2908)
    at ../nss/getXXbyYY_r.c:315
#46 0x00007f89909d6b77 in grantpt (fd=fd@entry=5) at
../sysdeps/unix/grantpt.c:152
#47 0x00007f8990a9394e in __GI_openpty (amaster=0x60c2bd94,
aslave=0x60c2bd98, name=0x0, termp=0x0, winp=0x0) at openpty.c:103
#48 0x00000000604a1f65 in openpty_cb (arg=0x60c2bd94) at arch/um/os-
Linux/sigio.c:407
#49 0x00000000604a58d0 in start_idle_thread (stack=0x60c28000
<init_thread_info>, switch_buf=0x60c31e08 <init_task+4936>) at
arch/um/os-Linux/skas/process.c:598
#50 0x0000000060004a3d in start_uml () at
arch/um/kernel/skas/process.c:45
#51 0x00000000600047b2 in linux_main (argc=1624806843, argv=0x40709000)
at arch/um/kernel/um_arch.c:334
#52 0x000000006000574f in main (argc=5, argv=0x7ffe3e7a4c98, envp=0x35)
at arch/um/os-Linux/main.c:144
(gdb) 

```


-- 
Ritesh Raj Sarraf | http://people.debian.org/~rrs
Debian - The Universal Operating System

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