Re: WARNING in set_restore_sigmask

[Thomas Gleixner]

Dmitry,

On Fri, 29 Jan 2016, Dmitry Vyukov wrote:
> WARNING: CPU: 2 PID: 10905 at ./arch/x86/include/asm/thread_info.h:236
> sigsuspend+0x18e/0x1f0()
> Modules linked in:
> CPU: 2 PID: 10905 Comm: syz-executor Not tainted 4.5.0-rc1+ #300
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  00000000ffffffff ffff88006139fe38 ffffffff82be118d 0000000000000000
>  ffff88006d054740 ffffffff867387e0 ffff88006139fe78 ffffffff813536d9
>  ffffffff813839ce ffffffff867387e0 00000000000000ec 0000000020000000
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82be118d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>  [<ffffffff813536d9>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:482
>  [<ffffffff81353909>] warn_slowpath_null+0x29/0x30 kernel/panic.c:515
>  [<     inline     >] set_restore_sigmask
> ./arch/x86/include/asm/thread_info.h:236
>  [<ffffffff813839ce>] sigsuspend+0x18e/0x1f0 kernel/signal.c:3513
>  [<     inline     >] SYSC_rt_sigsuspend kernel/signal.c:3533
>  [<ffffffff81387d7c>] SyS_rt_sigsuspend+0xac/0xe0 kernel/signal.c:3523
>  [<ffffffff86653236>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> ---[ end trace da5c27e3b7defd96 ]---

That could be just a spurious wakeup of unknown provenience. The sigsuspend
code has no protection against those. I can't see why that happens ...

> Unfortunately I cannot reproduce it. But the only two programs that

I would be helpful if you could run your fuzzers with a minimal set of trace
points enabled (raw_syscalls, sched events) and set
/proc/sys/kernel/traceoff_on_warning to 1, so the trace freezes when a warning
is triggered.

That might give us at least some insight into these one off issues.

Thanks,

	tglx