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

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Message-ID: <20190710140421.GP3402@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Jul 2019 16:04:21 +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 Tue, Jul 09, 2019 at 03:48:19PM +0200, Frederic Weisbecker wrote:
> 
> Syzbot has found a breakpoint overcommit issue:
> 
> https://lore.kernel.org/lkml/000000000000639f6a0584d11b82@google.com/
> 
> It took me a long time to find out what the actual root problem was. Also
> its reproducer only worked on a few month old kernel but it didn't feel like
> the issue was actually solved.
> 
> I eventually cooked a reproducer that works with latest upstream, see in
> the end of this message.
> 
> The fix is just a few liner but implies to shut down the context swapping
> optimization for contexts containing breakpoints.
> 
> Also I feel like uprobes may be concerned as well as it seems to make use
> of event.hw->target after pmu::init().

Can't we simply swizzle event.hw->target along too?