Re: [lkp-robot] [printk] c162d5b433: BUG:KASAN:use-after-scope_in_c

["Hao, Shun" <shun.hao@intel.com>]

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sorry for missing the attached script in original mail, here to add it.

On Thu, 2018-03-01 at 08:47 +0000, Dmitry Vyukov wrote:
> On Thu, Mar 1, 2018 at 2:37 AM, Sergey Senozhatsky
> <sergey.senozhatsky@gmail.com> wrote:
> > Hello,
> > 
> > Cc-ing Dmitry Vyukov and kasan-dev on this.
> > 
> > On (02/28/18 16:59), Petr Mladek wrote:
> > [..]
> > > > > 
> > > > > [    0.003333] BUG: KASAN: use-after-scope in
> > > > > console_unlock+0x185/0x960
> > > > > [    0.003333] BUG: KASAN: use-after-scope in
> > > > > console_unlock+0x185/0x960
> > > > 
> > > > Is there any change to get disassembly of console_unlock() from
> > > > the
> > > > problematic build?
> > > > 
> > > > I have troubles to reproduce this myself. Also I was not able
> > > > to find any
> > > > bug just by looking into the code yet. The disassembly might
> > > > help
> > > > a lot here.
> > > > 
> > > > 
> > > > Interesting symptoms (for myself and other debuggers):
> > > > 
> > > > The lines are duplicated. Therefore it happened when real
> > > > console was registered and before the early console was
> > > > unregistered.
> > > > See also the full dmesg for these actions. The related printk
> > > > messages
> > > > are right after the KASAN report.
> > > > 
> > > > I wonder if it is unsafe to pass the console_lock via
> > > > console_trylock_spinnning() from console_unlock() called
> > > > in register_console(). I do not see any problem but I might
> > > > be blind.
> > 
> > I'm not sure it we actually have concurrent printks at that state
> > yet,
> > might be too early for any printk offloading. The backtrace still
> > makes no sense to me at all, tho. We had this report twice,
> > probably,
> > already (even before the offloading patchset, if I'm not mistaken).
> > 
> > https://marc.info/?l=linux-kernel&m=151200883525299
> > 
> > [..]
> > > I feel lost a bit.
> > 
> > Yeah... can't understand what's going on there.
> > 
> > The last time kasan didn't like this part
> > 
> > [    0.003333]  ? console_unlock+0x605/0xcc0:
> >                               atomic_read at
> > arch/x86/include/asm/atomic.h:27
> >                                (inlined by) static_key_count at
> > include/linux/jump_label.h:191
> >                                (inlined by) static_key_false at
> > include/linux/jump_label.h:201
> >                                (inlined by) trace_console_rcuidle
> > at include/trace/events/printk.h:10
> >                                (inlined by) call_console_drivers at
> > kernel/printk/printk.c:1556
> >                                (inlined by) console_unlock at
> > kernel/printk/printk.c:2233
> > 
> > complaining that there was a write of size 4... at atomic_read().
> > 
> > Now it's reporting that the write of size 1 was out of scope.
> > 
> > > I am really curious what code is proceed on the line
> > > console_unlock+0x185/0x960.
> > 
> > Agreed.
> > 
> > On my system 0x185/0x960 is somewhere around
> > 
> > 
> >      191e:       89 d7                   mov    %edx,%edi
> >      1920:       e8 06 e7 ff ff          callq  2b <log_next>
> >      1925:       48 89 2d 00 00 00
> > 00    mov    %rbp,0x0(%rip)        # 192c <console_unlock+0x17f>
> >      192c:       89 05 00 00 00
> > 00       mov    %eax,0x0(%rip)        # 1932 <console_unlock+0x185>
> > > >   1932:       eb a9                   jmp    18dd
> > > > <console_unlock+0x130>
> > 
> >      1934:       8b 35 00 00 00
> > 00       mov    0x0(%rip),%esi        # 193a <console_unlock+0x18d>
> >      193a:       b9 00 04 00 00          mov    $0x400,%ecx
> >      193f:       4c 89 ef                mov    %r13,%rdi
> >      1942:       31 ed                   xor    %ebp,%ebp
> > 
> > 
> > That jmp 18dd after log_next() is a `goto skip' in
> > suppress_message_printing() branch
> > 
> > skip:
> >                 if (console_seq == log_next_seq)
> >                         break;
> > 
> >                 msg = log_from_idx(console_idx);
> >                 if (suppress_message_printing(msg->level)) {
> >                         /*
> >                          * Skip record we have buffered and already
> > printed
> >                          * directly to the console when we received
> > it, and
> >                          * record that has level above the console
> > loglevel.
> >                          */
> >                         console_idx = log_next(console_idx);
> >                         console_seq++;
> > > >                      goto skip;
> > 
> >                 }
> > 
> > 
> > As far as I can tell.
> 
> 
> Hi Shun,
> 
> The report says "job-script is attached in this email", but I don't
> see it attached. Did you forget to attach it? How can I reproduce
> this
> exact build?
> Could you post a symbolized report with inlines frames?

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