linux-kernel - Re: [PATCH 0/2] perf/hw_breakpoint: Fix breakpoint overcommit issue

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Date:   Mon, 15 Jul 2019 14:47:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        syzbot+370a6b0f11867bf13515@...kaller.appspotmail.com,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 0/2] perf/hw_breakpoint: Fix breakpoint overcommit issue

On Thu, Jul 11, 2019 at 12:53:05PM +0200, Peter Zijlstra wrote:
> > I wish we could use event->ctx->task instead but on pmu::init() there
> > is no ctx yet (we could pass the task in parameter though) 
> 
> Right, that should be fairly easy.
> 
> > and on event->destroy() it's TASK_TOMBSTONE and retrieving the task at
> > that time would be non trivial.
> 
> Well, right, we can maybe make TOMBSTONE be the LSB instead of the whole
> word, then we can recover the task pointer... *yuck* though.

Something like the attached, completely untested patches.

I didn't do the hw_breakpoint bit, because I got lost in that, but this
basically provides what you asked for I think.


View attachment "peterz-perf-task-1.patch" of type "text/x-diff" (3190 bytes)

View attachment "peterz-perf-task-2.patch" of type "text/x-diff" (974 bytes)

View attachment "peterz-perf-task-3.patch" of type "text/x-diff" (5488 bytes)

View attachment "peterz-perf-task-4.patch" of type "text/x-diff" (2175 bytes)

View attachment "peterz-perf-task-5.patch" of type "text/x-diff" (35551 bytes)

View attachment "peterz-perf-task-6.patch" of type "text/x-diff" (1359 bytes)