linux-kernel - Stupid futex question

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Date:	Thu, 18 Feb 2010 09:04:22 -0500
From:	Valdis.Kletnieks@...edu
To:	linux-kernel@...r.kernel.org
Subject: Stupid futex question - 2.6.33-rc7-mmotm0210

Kernel: x86_64 2.6.33-rc7-mmotm0210

I'm debugging a problem where pulseaudio is getting killed with a SIGKILL
out of the blue.  It appears to be a problem where pulseaudio sets
RLIMIT_RTTIME and the bound gets exceeded.  Analysis with 'top' shows
a short spike of 96% system time, and the tail end of strace shows this:

[pid 25065] 01:50:20.371484 ioctl(28, USBDEVFS_CONTROL, 0x7fd3d76f630c) = 0 <0.000015>
[pid 25065] 01:50:20.371548 ioctl(28, 0x40045532, 0x7fd3d76f636c) = 0 <0.000016>
[pid 25065] 01:50:20.371611 open("/dev/snd/pcmC0D0p", O_RDWR|O_NONBLOCK|O_CLOEXEC <unfinished ...>
[pid 25064] 01:50:20.371678 <... write resumed> ) = 8 <0.002104>
[pid 25064] 01:50:20.371718 futex(0xc2ec00, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
[pid 25066] 01:50:21.408392 +++ killed by SIGKILL +++
PANIC: handle_group_exit: 25066 leader 25064
[pid 25065] 01:50:21.408442 +++ killed by SIGKILL +++
PANIC: handle_group_exit: 25065 leader 25064
01:50:21.420354 +++ killed by SIGKILL +++

thread 25064 apparently gets gunned down due to RTTIME because it spent a whole
second in a futex() call - is it reasonable for futex() to not return for that
long?

In other words - kernel bug because futex() should return, or pulseaudio bug
for not understanding futex() can snooze a while?

If a kernel bug, anybody got a better idea than nuking the RLIMIT_RTTIME call,
waiting for it to repeat (takes between 1 minute and 1 hour or so), and
whomping it a few times with sysrq-T?

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