Re: [PATCH] Fix kexec abort due to IPI from panic().

[Eric W. Biederman]

Seiji Aguchi <seiji.aguchi@xxxxxxx> writes:

> Hi,
>
> I'm Seiji Aguchi.
> I work for Hitachi Data Systems.
> It's a first time to send a patch to lkml.
> Nice to meet you.
>  
> I found an issue in kexec.
> Please give me your comments and suggestions.
>  
> Kexec abort when two cpus panic at the same time.
> An example scenario:
> 1. Two cpus panic at the same time .
> 2. One cpu ,cpu0, get kexec_mutex in crash_kexec().
> 3. The other cpu ,cpu1, can't get kexec_mutex and return from crash_kexec().
> 4. Cpu0 runs kmsg_dump(KMSG_DUMP_KEXEC).
> 5. Cpu1 can't get dump_list_lock and return from kmsg_dump(KMSG_DUMP_PANIC).
> 6. Cpu1 runs smp_send_stop() in panic() and sends IPI to other cpus.
> 7. Cpu0 may receive IPI from cpu1 while running kmsg_dump(KMSG_DUMP_KEXEC),
>    crash_setup_regs(), or crash_save_vmcore().
>  
> We can solve this issue by disabling external interrupt while getting kexec_mutex 
> in crash_kexec().

Disabling interrupts is fine, I thought we did that already at some
point.  However that call to kmsg_dump(KMSG_DUMP_KEXEC) is a bug as it
introduces locks into a path that should not be taking locks.  Please
remove that broken kmsg_dump call as well.

Nothing in the crash_kexec path should even have the option of blocking.

Eric
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