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SubjectRe: HR timers prevent an itimer from generating EINTR?
(cc's added)

(it's a regression)

(it has a testcase!)

On Fri, 04 Sep 2009 17:26:35 -0400
Mike Heffner <mikeh@fesnel.com> wrote:

> Summary:
>
> Mixing HR timers with itimers occasionally hides an EINTR from a
> blocking syscall.
>
>
> Description:
>
> In my test program I have a High Resolution timer firing every one
> second (with SA_RESTART) and I set an itimer (without SA_RESTART) to
> fire after three seconds. I then execute a blocking system call (flock
> in this case) and expect the three second itimer to interrupt the system
> call with EINTR. However, I frequently notice that the itimer will fire
> but it will not interrupt the blocking system call. There appears to be
> a race between the HR timer firing and the itimer firing. If I offset
> the HR timer frequency by a half second, the itimer always interrupts
> the system call.
>
> Kernel version:
>
> These kernels both demonstrate the condition:
>
> 2.6.29.6-217.2.16.fc11.x86_64
> and
> 2.6.30.5-43.fc11.x86_64
>
>
> I do not see this condition on:
>
> 2.6.18-53.el5
>
>
> Test program:
>
> The following program illustrates this condition:
>
> http://github.com/mheffner/scripts/commits/master/hrtimer_vs_itimer.c
>
>
> Is this behavior expected?
>
>



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