From nobody Mon Feb 9 15:27:10 2026 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 8E90F22AE65 for ; Wed, 5 Feb 2025 10:25:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738751137; cv=none; b=e9NBS1RRYBYD3L7y++3rJACJMH/0Y8i75bii0qDgckxG7IkzWzbRLZz+88PmfLS8coKcs2rm17VhHACXfBe4WB9Dt3RqxuZEMEnDbkGx62N5EBhOfN/Muv/H2LSJCtLUTbiIOcdf8tRI8fUJjCkRO5mAqglBvD7XaeFSdzA/xQg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738751137; c=relaxed/simple; bh=nl/E7IbifIHY4saIGLrcUyqLZKw5Y4dVMLE4DYop58Y=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=lVugHw5EslAkKuPeszwceVGWSlLDP7LvNGh1EuDUDBVp/5Fc2yKInZQHbFD6SUrqA3bPFAE4sFb/oGR6tTphfEabhTzPTNU5AYANYzVeMOBQySK2adK/5KqlEbzqsD4zCjbJsg5gXZtXP2MCb77tYTbVKEHy278K3Bh1PktbnL8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=pza+EoGK; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pza+EoGK" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=zvAjMRogCzZXBg0SQLthP0VbH9NxSHSRwZYyo2uheI4=; b=pza+EoGKR8cpT/KN8sT5/+L4pD 6Zp2YqczUFeL6npG5/mfBsDhyGZGdPholkSKZpc0NV6diavYr8G6KgkT6KrVrLZifPQBKqSCngLGk 8MLiT3hqDty7zA5MmwPT3w/3UBdZNY5vgkJ1bPF9PR3YtGHUTBrxvlVCI4aVlnOjF4zlpjxcSnjV0 7rGwqkg0kx1CqBQKqBX9bgQPWYvMa6lYlLabQZ/h5tnOfM3Tmoth9COyPByTSGfM3W5JBOSm4CBRD FR4cO6D7x7MubuzV+4MWbVlLDFc4/P5bxXuHNQsEQww3sXUDnVEpwdwl67/G84FAUiiNMFaJ7nNvj RNfWi5hQ==; Received: from 77-249-17-89.cable.dynamic.v4.ziggo.nl ([77.249.17.89] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tfcb4-00000004GQ9-2U9P; Wed, 05 Feb 2025 10:25:30 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 0) id 0A3863085E6; Wed, 5 Feb 2025 11:25:28 +0100 (CET) Message-ID: <20250205102450.672685519@infradead.org> User-Agent: quilt/0.66 Date: Wed, 05 Feb 2025 11:21:42 +0100 From: Peter Zijlstra To: mingo@kernel.org, ravi.bangoria@amd.com, lucas.demarchi@intel.com Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, willy@infradead.org, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com Subject: [PATCH v2 22/24] perf: Remove retry loop from perf_mmap() References: <20250205102120.531585416@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" AFAICT there is no actual benefit from the mutex drop on re-try. The 'worst' case scenario is that we instantly re-gain the mutex without perf_mmap_close() getting it. So might as well make that the normal case. Reflow the code to make the ring buffer detach case naturally flow into the no ring buffer case. Signed-off-by: Peter Zijlstra (Intel) --- kernel/events/core.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6667,27 +6667,32 @@ static int perf_mmap(struct file *file, return -EINVAL; =20 WARN_ON_ONCE(event->ctx->parent_ctx); -again: mutex_lock(&event->mmap_mutex); + if (event->rb) { if (data_page_nr(event->rb) !=3D nr_pages) { ret =3D -EINVAL; goto unlock; } =20 - if (!atomic_inc_not_zero(&event->rb->mmap_count)) { + if (atomic_inc_not_zero(&event->rb->mmap_count)) { /* - * Raced against perf_mmap_close(); remove the - * event and try again. + * Success -- managed to mmap() the same buffer + * multiple times. */ - ring_buffer_attach(event, NULL); - mutex_unlock(&event->mmap_mutex); - goto again; + rb =3D event->rb; + ret =3D 0; + goto unlock; } =20 - rb =3D event->rb; - goto unlock; + /* + * Raced against perf_mmap_close()'s + * atomic_dec_and_mutex_lock() remove the + * event and continue as if !event->rb + */ + ring_buffer_attach(event, NULL); } + } else { /* * AUX area mapping: if rb->aux_nr_pages !=3D 0, it's already