Re: [PATCH 6/8] blackfin: Fix possible race on task->mm

[Oleg Nesterov]

On 02/07, Anton Vorontsov wrote:
>
> Even when in atomic context, grabbing irqsave variant of tasklist lock
> is not enough to protect task->mm from disappearing on SMP machines.
> Instead, we have to grab the task lock.

Yes, but afaics there is no reason for write_lock_irqsave(tasklist).
read_lock() should be enough.

I know nothing about arch/blackfin/ but in fact this looks simply wrong.

For example. sysrq_showregs_othercpus() does smp_call_function(showacpu)
and showacpu() show_stack()->decode_address(). Now suppose that IPI
interrupts the task holding read_lock(tasklist).

Mike?

Oleg.

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