Re: kretprobe not consistently being triggered for sys_futex calls?


Paul Chaignon
 

On Tue, Feb 12, 2019 at 07:02:58AM -0800, Ashley wrote:
So I upgraded my kernel version to 5.0.0-rc6, and it seems to consistently
work perfectly now, even with a much higher density of futex calls than I
was working with before.

I'm still curious what the issue is, and I sadly can't say with any
confidence that it's definitely the kernel version, since I accidentally
broke my filesystem trying to resize it and had to make a fresh VM, so I
may have different BCC or dependency versions installed on this machine,
but I'm hoping to find time to dig a bit more in a few weeks to see if I
can determine what was going on here.
bcc now supports the maxactive kretprobe parameter [1], so if you want to
test whether a higher maxactive value solves the issue you had, it's as
easy as calling BPF.attach_kretprobe with a maxactive=your_value argument.

1 - https://github.com/iovisor/bcc/pull/2224


Thanks again for the help, Paul! I wouldn't have considered playing with
the kernel version without realising it was working fineĀ  for the kernel
module.

Regards,
Ashley

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