Messages in this thread | | | Date | Wed, 26 Oct 2011 20:58:38 +0200 | From | Oleg Nesterov <> | Subject | Re: [RESEND] [RFC][PATCH X86_32 1/2]: Call do_notify_resume() with interrupts enabled |
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On 10/26, Russell King wrote: > > I've been toying with a similar patch for ARM, but I keep feeling uneasy > about having interrupts enabled in this path (even though they get enabled > in the depths of the signal handling code.) > > I worry about are race condition like the following: > > syscall enter > ... > syscall returns -ERESTARTNOHAND > check for signal > signal pending, but no handler, setup for restart > interrupt happens, sets need_resched > need_resched set > switch to another thread > ... > something happens which queues SIGIO > switch back to this thread
I don't understand how "interrupts disabled" can help... A signal can come without preempt_schedule().
> check for signal > signal pending, has handler, but we've setup for a restart > return to userspace > run SIGIO handler > restart syscall > > This feels like it violates the expectations of the syscall being > restarted - which explicitly asks to be restarted only if there wasn't > a handler run.
But this doesn't differ from the case when this signal comes after the sycall was already restarted?
> However, that doesn't solve the (probably unsolvable) case where an > ERESTARTSYS syscall is interrupted by a SA_RESTART-marked handler, and > while that handler is running it is then interrupted by a non-SA_RESTART- > marked handler. I think that is far too an obscure case to care about > though.
If I understand correctly, this was already discussed:
Re: HR timers prevent an itimer from generating EINTR? http://marc.info/?l=linux-kernel&m=125384722012869
Unfortunately, marc.info doesn't show the authoritative reply from Roland, but he agreed with "not a problem".
Or I misunderstood?
Oleg.
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