Re: [PATCH 1/8] perf: Allow to block process in syscall tracepoints

["Dmitry V. Levin" <ldv@altlinux.org>]

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On Wed, Dec 12, 2018 at 08:26:39PM -0500, Steven Rostedt wrote:
> On Thu, 13 Dec 2018 03:39:38 +0300, wrote:
> 
> > btw, I didn't ask for the implementation to be ugly.
> > You don't have to introduce polling into the kernel if you don't want to,
> > userspace is perfectly capable of invoking wait4(2) in a loop.
> > Just block the tracee, notify the tracer, and let it pick up the pieces.
> 
> Note, there's been some discussion offlist to only have perf set a flag
> when it dropped an event and have the ptrace code do the heavy lifting
> of blocking the task and waking it back up. I think that would be a
> cleaner solution and wont muck with perf as badly.

Yes, if perf could be instructed to invoke something like
tracehook_report_syscall_entry/exit when it drops the event
of entering/exiting syscall, that should probably be enough
for the ptracer to do the recovery.


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ldv

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