Hello Vikram, Putting "linux-arch" on cc... On Thu, 28 Jun 2012 16:43:05 -0700 Vikram Mulukutla <markivx@xxxxxxxxxxxxxx> wrote: > panic_lock is meant to ensure that panic processing takes > place only on one cpu; if any of the other cpus encounter > a panic, they will spin waiting to be shut down. > > However, this causes a regression in this scenario: > > 1. Cpu 0 encounters a panic and acquires the panic_lock > and proceeds with the panic processing. > 2. There is an interrupt on cpu 0 that also encounters > an error condition and invokes panic. > 3. This second invocation fails to acquire the panic_lock > and enters the infinite while loop in panic_smp_self_stop. > > Thus all panic processing is stopped, and the cpu is stuck > for eternity in the while(1) inside panic_smp_self_stop. > > To address this, disable local interrupts with > local_irq_disable before acquiring the panic_lock. This will > prevent interrupt handlers from executing during the panic > processing, thus avoiding this particular problem. Looks good to me. I re-read the panic lock discussion and in fact one version of my patch also disabled interrupts: http://lists.infradead.org/pipermail/kexec/2011-October/005695.html I think the reason why we later took a version with irqs enabled was that we did not think about the scenario you described above and we wanted to make the change as less intrusive as possible. But I am not really sure about that. Regarding you patch: Perhaps we could use spin_trylock_irq() instead of local_irq_disable() and spin_lock(). Michael -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
