Re: [PATCH -tip 0/2] fix lock inversion in lockless sys_times()

[Peter Zijlstra]

On Fri, Sep 12, 2014 at 09:12:13AM -0400, riel@xxxxxxxxxx wrote:
> The sig->stats_lock nests inside the tasklist_lock and the
> sighand->siglock in __exit_signal and wait_task_zombie.
> 
> However, both of those locks can be taken from irq context,
> which means we need to use the interrupt safe variant of
> read_seqbegin_or_lock. This blocks interrupts when the "lock"
> branch is taken (seq is odd), preventing the lock inversion.
> 
> On the first (lockless) pass through the loop, irqs are not
> blocked.
> 
> This fixes the lockdep complaints that Stanislaw reported.
> 

Thanks Rik
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