linux-kernel - Re: [PATCH v10 06/14] unwind_user/deferred: Add deferred unwinding interface

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Message-ID: <20250618113831.1e26bb8f@gandalf.local.home>
Date: Wed, 18 Jun 2025 11:38:31 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Ingo Molnar <mingo@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Thomas
 Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>, Indu
 Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>, Beau
 Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton
 <akpm@...ux-foundation.org>
Subject: Re: [PATCH v10 06/14] unwind_user/deferred: Add deferred unwinding
 interface

On Wed, 18 Jun 2025 11:37:06 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> > What about two CPUs managing to request an unwind at exactly the same
> > time?  
> 
> It's mapped to a task. As long as each timestamp is unique for a task it
> should be fine. As the trace can record the current->pid along with the
> timestamp to map to the unique user space stack trace.
> 
> As for resolution, as long as there can't be two system calls back to back
> within the same time stamp. Otherwise, yeah, we have an issue.

I'll add a comment that states this as a constraint.

-- Steve