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Date: Fri, 04 Sep 2009 17:26:35 -0400 From: Mike Heffner <mikeh@...nel.com> To: linux-kernel@...r.kernel.org Subject: HR timers prevent an itimer from generating EINTR? 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? Cheers, Mike -- Mike Heffner <mikeh@...nel.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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