Re: [BUG] uml panics with "Segfault with no mm" in v3.19-rc

[Geert Uytterhoeven]

On Wed, Dec 10, 2014 at 11:49 AM, Richard Weinberger <richard@xxxxxx> wrote:
> Am 10.12.2014 um 11:46 schrieb Miklos Szeredi:
>> The guilty commit is:
>>
>>   00f634bc522d "asm-generic: add generic futex for !CONFIG_SMP"
>
> Thanks a lot Miklos!
> Your bisecting faster than I do.
>
> Let's dig into the issue!

Do you need "select HAVE_FUTEX_CMPXCHG if FUTEX"?

Cfr. commit e571c58f313d35c5 ("m68k: Skip futex_atomic_cmpxchg_inatomic()
test") and commit 03b8c7b623c80af2 ("futex: Allow architectures to skip
futex_atomic_cmpxchg_inatomic() test").

BTW, I still think the real problem is the wrong address space, cfr.
"[PATCH/RFC] futex: Switch to USER_DS for futex test"
(http://www.spinics.net/lists/linux-m68k/msg06597.html), so you may also
want to try that.
However, that caused problems on s390, as it ran too early:
http://permalink.gmane.org/gmane.linux.kernel.next/30165

>> And the backtrace:
>>
>> #0  0x00007ffff7866457 in kill () from /lib64/libc.so.6
>> #1  0x000000006002a454 in uml_abort () at arch/um/os-Linux/util.c:93
>> #2  0x000000006002a7e5 in os_dump_core () at arch/um/os-Linux/util.c:148
>> #3  0x000000006001b48a in panic_exit (self=<optimized out>, unused1=<optimized out>, unused2=<optimized out>) at arch/um/kernel/um_arch.c:240
>> #4  0x000000006004e4df in notifier_call_chain (nl=<optimized out>, val=6, v=0xffffffff, nr_to_call=-1, nr_calls=0x0) at kernel/notifier.c:93
>> #5  0x000000006004e558 in __atomic_notifier_call_chain (nr_calls=<optimized out>, nr_to_call=<optimized out>, v=<optimized out>, val=<optimized out>, nh=<optimized out>) at kernel/notifier.c:183
>> #6  atomic_notifier_call_chain (nh=<optimized out>, val=<optimized out>, v=<optimized out>) at kernel/notifier.c:193
>> #7  0x0000000060238570 in panic (fmt=<optimized out>) at kernel/panic.c:133
>> #8  0x000000006001ad91 in segv (fi=..., ip=1610803493, is_user=<optimized out>, regs=0x602c1840 <cpu0_irqstack+6208>) at arch/um/kernel/trap.c:218
>> #9  0x000000006001b0f8 in segv_handler (sig=<optimized out>, unused_si=<optimized out>, regs=<optimized out>) at arch/um/kernel/trap.c:191
>> #10 0x0000000060029238 in sig_handler_common (sig=11, si=0x602c1d30 <cpu0_irqstack+7472>, mc=<optimized out>) at arch/um/os-Linux/signal.c:44
>> #11 0x0000000060029304 in sig_handler (sig=<optimized out>, si=<optimized out>, mc=<optimized out>) at arch/um/os-Linux/signal.c:231
>> #12 0x0000000060028dfd in hard_handler (sig=<optimized out>, si=0x6, p=<optimized out>) at arch/um/os-Linux/signal.c:165
>> #13 <signal handler called>
>> #14 memcpy () at arch/x86/um/../lib/memcpy_64.S:160
>> #15 0x000000006001c13d in copy_from_user (to=0x61c49e28, from=<optimized out>, n=<optimized out>) at arch/um/kernel/skas/uaccess.c:145
>> #16 0x0000000060072618 in futex_atomic_cmpxchg_inatomic (newval=<optimized out>, oldval=<optimized out>, uaddr=<optimized out>, uval=<optimized out>) at include/asm-generic/futex.h:109
>> #17 cmpxchg_futex_value_locked (curval=0x61c49e28, uaddr=0x0, uval=<optimized out>, newval=<optimized out>) at kernel/futex.c:596
>> #18 0x0000000060008b70 in futex_detect_cmpxchg () at kernel/futex.c:3020
>> #19 futex_init () at kernel/futex.c:3043
>> #20 0x00000000600166ba in do_one_initcall (fn=0x60008adf <futex_init>) at init/main.c:791

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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