Re: [Crash-utility] infinite loop in crash due to double-NMI on x86_64 system
----- "Petr Tesarik" <ptesarik(a)suse.cz> wrote:
Silacci, Lucas píše v Po 28. 06. 2010 v 17:26 -0400:
> The dumpsw_notify function is part of a driver that was added to our
> systems to trigger kernel panics when an NMI occurs. In the version of
> the kernel we are using (SLES 10 SP1) this was necessary to cause an
> actual panic to happen and a dump to be saved when an NMI occurred
> (especially due to a dump switch being pressed, hence the name).
>
> That driver registers a callback (dumpsw_notify) into the die_chain and
> calls panic() if the die code is a DIE_NMI.
Hi,
my opinion is that a NMI is ... well, a non-maskable interrupt. Which
means there is nothing the kernel could possibly do to prevent the NMI
handler itself from being interrupted by another NMI. Whatever the
reason for it.
Really? According to the AMD x86_64 manual -- note the "Masking" section:
8.3.3 NMI-Non-Maskable-Interrupt Exception (Vector 2)
An NMI exception occurs as a result of system logic signalling a
non-maskable interrupt to the processor.
Error Code Returned: None.
Program Restart: NMI is an interrupt. The processor recognizes an NMI
at an instruction boundary. The saved instruction pointer points to the
instruction immediately following the boundary where the NMI was recognized.
Masking: NMI cannot be masked. However, when an NMI is executed by the
processor, recognition of subsequent NMIs are disabled until an IRET
instruction is executed.
And looking at the backtrace, I'm still having a hard time understanding how
it was possible. What am I missing?
Dave
Having the crash utility loop forever on such dumps is annoying, at
the
very least. And I imagine, such hangs could cause quite some headache to
Louis Bouchard. ;)
Just my $0.02,
Petr Tesarik
PID: 0 TASK: ffffffff8038c340 CPU: 0 COMMAND:
"swapper"
#0 [ffffffff8046dc50] machine_kexec at ffffffff8011a95b
#1 [ffffffff8046dd20] crash_kexec at ffffffff80154351
#2 [ffffffff8046dde0] panic at ffffffff801327fa
#3 [ffffffff8046ded0] dumpsw_notify at ffffffff8831c0c3
#4 [ffffffff8046dee0] notifier_call_chain at ffffffff8032481f
#5 [ffffffff8046df00] default_do_nmi at ffffffff80322fab
#6 [ffffffff8046df40] do_nmi at ffffffff80323365
#7 [ffffffff8046df50] nmi at ffffffff8032268f
[exception RIP: smp_send_stop+84]
RIP: ffffffff80116e44 RSP: ffffffff8046ddd8 RFLAGS: 00000246
RAX: 00000000000000ff RBX: ffffffff8831c1f8 RCX: 000041049c7256e8
RDX: 0000000000000005 RSI: 000000005238a938 RDI: 00000000002896a0
RBP: ffffffff8046df08 R8: 00000000000040fb R9: 000000005238a7e8
R10: 0000000000000002 R11: 0000ffff0000ffff R12: 000000000000000c
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
--- <NMI exception stack> ---
#8 [ffffffff8046ddd8] smp_send_stop at ffffffff80116e44