From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D155028FA85; Wed, 18 Jun 2025 15:38:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750261111; cv=none; b=fUJnzXWC9OAst59j2i4s7kakv+47uZvi7Iw0Kj79DnPggh/KTY+OSdvl+UTktWSeI1mCzYG3LofVN+ThRRRDbxhTrGQ+BapS65m2MOVj0MNne/gfjNdWQA9WFt9bdk5JqidKv6Ed236ZXGDpnFfjahzCOoWWGQBHPp0aAUm8AlY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750261111; c=relaxed/simple; bh=cKSFSoxnitAjZGgvNgqUq5XLSDt0L0l7BTH00fNZQyY=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ojpF50eljr42vqxQsuFyEJ5Q3jas6WRJB8JG4mnw9EOLcoDZjCEgskEqtY4xr0e4ucYNsN7Ps5yxUHBN3lP6sR1X4TJdEa/fZ5+EQtT9TOEDfpFjLXucwZ966nyWy865MMtjEKfR8WeMhGASUgKlS8BH6elHXEIwCyilEUxtAkE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 513DF8030A; Wed, 18 Jun 2025 15:38:27 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf15.hostedemail.com (Postfix) with ESMTPA id 8AC9A18; Wed, 18 Jun 2025 15:38:23 +0000 (UTC) Date: Wed, 18 Jun 2025 11:38:31 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, x86@kernel.org, Masami Hiramatsu , Mathieu Desnoyers , Josh Poimboeuf , Ingo Molnar , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Andrii Nakryiko , Indu Bhagat , "Jose E. Marchesi" , Beau Belgrave , Jens Remus , Linus Torvalds , Andrew Morton Subject: Re: [PATCH v10 06/14] unwind_user/deferred: Add deferred unwinding interface Message-ID: <20250618113831.1e26bb8f@gandalf.local.home> In-Reply-To: <20250618113706.2eb46544@gandalf.local.home> References: <20250611005421.144238328@goodmis.org> <20250611010428.770214773@goodmis.org> <20250618142000.GS1613376@noisy.programming.kicks-ass.net> <20250618113706.2eb46544@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 8AC9A18 X-Stat-Signature: 9iom6z8i66zini513gfg4cfdddsds1ej X-Rspamd-Server: rspamout05 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/ghWbw4OhlNrQUhRvEjr4WTJdnB8xIu9E= X-HE-Tag: 1750261103-260494 X-HE-Meta: U2FsdGVkX1+Zb3aFmTig2sc9oHDxGzoxPAPVRMMDMdGsNcMwCVfCIq9cb5qeHdR9cf1rgXOoKdMI11YFVKGsQW7Hp6dXNkA2V82gofI8VLhDAr30CUBkbuwOSuRwOP82/pPxKL+3NYChbGNQ5PMTNiIoUD+VWuaHz8vouUcyKD525ahAgre4dQ2bMdbG/VBsWaTSUx1dLIJmwWwRxUz7gfm7PcbOWclEnyCBCTODpqi2ixk9w+ohsQrpMq4Ag6dm1YzrIJiv/kVmNCfiGI1uReR03BlrLa8TCyUsPJJfHxbE3j0II8hfVVeqKSxhmgQW8uyE22llU25FLW5ANafbO6wPFjB/KqmWKOa+Q1yB6DMK4voYlIeVQeH4S0vB1ydC On Wed, 18 Jun 2025 11:37:06 -0400 Steven Rostedt 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