Received-SPF: pass (google.com: domain of linux-kernel+bounces-138673-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Wed, 10 Apr 2024 15:47:02 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	Adrian Hunter <adrian.hunter@intel.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Ian Rogers <irogers@google.com>, Ingo Molnar <mingo@redhat.com>,
	Jiri Olsa <jolsa@kernel.org>, Marco Elver <elver@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Namhyung Kim <namhyung@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
Subject: Re: [PATCH v3 2/4] perf: Enqueue SIGTRAP always via task_work.
Message-ID: <20240410134702.dcWYciZB@linutronix.de>
References: <20240322065208.60456-1-bigeasy@linutronix.de>
 <20240322065208.60456-3-bigeasy@linutronix.de>
 <ZhRhn1B0rMSNv6mV@pavilion.home>
 <20240409085732.FBItbOSO@linutronix.de>
 <ZhU2YwettB6i6AMp@localhost.localdomain>
 <20240409134729.JpcBYOsK@linutronix.de>
 <ZhZ54XAcBt50WEnE@localhost.localdomain>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <ZhZ54XAcBt50WEnE@localhost.localdomain>

On 2024-04-10 13:37:05 [+0200], Frederic Weisbecker wrote:
> > Couldn't we either flush _or_ remove the task_work in perf_release()?
> 
> Right so the problem in perf_release() is that we may be dealing with task works
> of other tasks than current. In that case, task_work_cancel() is fine if it
> successes. But if it fails, you don't have the guarantee that the task work
> isn't concurrently running or about to run. And you have no way to know about
> that. So then you need some sort of flushing indeed.

Since perf_release() preemptible, a wait/sleep for completion would be
best (instead of flushing).

> Thanks.
> 
> > > Thanks.

Sebastian