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Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [BUG REPORT] Triggering a panic in an x86 virtual machine does not wait Content-Language: en-US To: Thomas Gleixner CC: , , , , , , , , , , yangerkun , Baoquan He , , Baokun Li References: <20230615193330.608657211@linutronix.de> <71578392-63ed-02a9-24da-2adf8cce38c7@huawei.com> <87ttui91jo.ffs@tglx> From: Baokun Li In-Reply-To: <87ttui91jo.ffs@tglx> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.174] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpeml500021.china.huawei.com (7.185.36.21) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/7/5 16:59, Thomas Gleixner wrote: > On Mon, Jul 03 2023 at 11:44, Baokun Li wrote: > >> When I manually trigger panic in a qume x86 VM with >> >>        `echo c > /proc/sysrq-trigger`, >> >>  I find that the VM will probably reboot directly, but the >> PANIC_TIMEOUT is 0. >> This prevents us from exporting the vmcore via panic, and even if we succeed >> in panic exporting the vmcore, the processes in the vmcore are mostly >> stop_this_cpu(). By dichotomizing we found the patch that introduced the >> behavior change >> >>    45e34c8af58f ("x86/smp: Put CPUs into INIT on shutdown if possible"), > Bah, I missed that this is used by crash too. So if this happens to be > invoked on an AP, i.e. not on CPU 0, then the INIT will reset the > machine. Fix below. > > Thanks, > > tglx > --- > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index ed2d51960a7d..e1aa2cd7734b 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -1348,6 +1348,14 @@ bool smp_park_other_cpus_in_init(void) > if (apic->wakeup_secondary_cpu_64 || apic->wakeup_secondary_cpu) > return false; > > + /* > + * If this is a crash stop which does not execute on the boot CPU, > + * then this cannot use the INIT mechanism because INIT to the boot > + * CPU will reset the machine. > + */ > + if (this_cpu) > + return false; > + > for_each_present_cpu(cpu) { > if (cpu == this_cpu) > continue; This patch does fix the problem of rebooting at panic, but the exported stack stays at stop_this_cpu() like below, instead of showing what the corresponding process is doing as before. PID: 681      TASK: ffff9ac2429d3080  CPU: 2    COMMAND: "fsstress"  #0 [ffffb00200184fd0] stop_this_cpu at ffffffff89a4ffd8  #1 [ffffb00200184fe8] __sysvec_reboot at ffffffff89a94213  #2 [ffffb00200184ff0] sysvec_reboot at ffffffff8aee7491 --- ---     RIP: 0000000000000010  RSP: 0000000000000018  RFLAGS: ffffb00200f8bd08     RAX: ffff9ac256fda9d8  RBX: 0000000009973a85  RCX: ffff9ac256fda078     RDX: ffff9ac24416e300  RSI: ffff9ac256fda9e0  RDI: ffffffffffffffff     RBP: ffff9ac2443a5f88   R8: 0000000000000000   R9: ffff9ac2422eeea0     R10: ffff9ac256fda9d8  R11: 0000000000549921  R12: ffff9ac2422eeea0     R13: ffff9ac251cd23c8  R14: ffff9ac24269a800  R15: ffff9ac251cd2150     ORIG_RAX: ffffffff8a1719e4  CS: 0206  SS: ffffffff8a1719c8 bt: WARNING: possibly bogus exception frame Do you know how this happened? I would be grateful if you could fix it. Thanks! -- With Best Regards, Baokun Li .