From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 186D137C10A; Sun, 9 Aug 2026 02:32:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786242738; cv=none; b=mXran7ZCU1zlSLwtiVMK2x9ifveHkjTcJD+UMWU0B3FPt50kveu++0mVPLzbK1GWPhBbP6ghfH/XDH1myy6RxbSbXVymC5z6qZRTNpBWJNVR7rjbLF/NYMD22LCrjjXV73T0Kbp4pol9FywZ/n9jewPqShyEe6pCl752RKLTUPQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786242738; c=relaxed/simple; bh=7lujbEOmldkRiLrS41CTuOilo6e/XBJd+Wp/yIsUFyQ=; h=Message-ID:Date:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=GiSkNocfIiS3uEyvj9Glb9UZ8btHtShUTtA45rM645B4oet7ji0gH89eshts+52E5tYMlpVuiUVEDO+7K8eUennrfrwTaQixOGWaH0mpwlkIkLLBIAbf6TkJX/JLTHowj1jIKe1bHQzsFnmz0Sdjy+YY8sbzRz8BhaV1LunyIU4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Q2e3LFQG; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Q2e3LFQG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2A9541F00A3E; Sun, 9 Aug 2026 02:32:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786242736; bh=RsZajquT8PdTHqA0S7T6sbbrTm5qKWASenU4d6SqLAk=; h=Date:From:To:Cc:Subject:References; b=Q2e3LFQG19dSfuy6kAfEAxyiE6Vu2O8mHOH9xigpsRTgTKoUK4OC7RsPQSiWx75T2 DblYojEGTo44Cr0fmfCyV5V+Xe9zIQoAzGwcwWVGCWvGUPjOtdAZkEMxJAe3PnONAb VQ6JFbn63ZlHDw39+2FNsNkgx65hQgyZAkY4zoZvObydSXNRohnGErdpN0zBvz+nKi HX1p0nSelUE83OMvzIaZ60BXGhriCRNl3ByL1eSXW567sxHnYRzPBFCrNVogejgBD3 p8vmKlEpeBRdXRC0MWjqb2eLfOiIHdXezDeKNj7tv9LXhsGm+fu1hqiI69T6DJjjHl uV9AIDJUMVPhA== Received: from rostedt by gandalf with local (Exim 4.99.4) (envelope-from ) id 1wstKo-00000001N5h-20N7; Sat, 08 Aug 2026 22:32:22 -0400 Message-ID: <20260809023222.338674181@kernel.org> User-Agent: quilt/0.69 Date: Sat, 08 Aug 2026 22:31:51 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , stable@vger.kernel.org, Tengda Wu Subject: [for-linus][PATCH 07/12] ring-buffer: Use current_context for safe per-CPU buffer swap References: <20260809023144.852271250@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Tengda Wu The ring_buffer_swap_cpu() function currently checks the per-CPU committing counter to determine if a buffer is actively being written to before performing the swap. However, there exists a race window where this check can be bypassed: ring_buffer_lock_reserve cpu_buffer = buffer->buffers[cpu]; // cpu_buffer_a rb_reserve_next_event rb_start_commit // inc committing if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {...} __rb_reserve_next rb_move_tail rb_end_commit(cpu_buffer); // dec committing => 0 /* interrupt hits here, successfully swaps! */ local_inc(&cpu_buffer->committing); ring_buffer_unlock_commit cpu_buffer = buffer->buffers[cpu]; // cpu_buffer_b rb_commit rb_end_commit RB_WARN_ON(cpu_buffer, !local_read(&cpu_buffer->committing)) // triggers warning The committing counter can temporarily drop to 0 during a single write operation (within rb_move_tail), creating a window where swap can succeed even though the write is still in progress. This leads to inconsistent buffer state and triggers the RB_WARN_ON in rb_commit(). Replace the committing counter check with current_context checks, which are set at the entry of ring_buffer_lock_reserve() and remain valid throughout the entire write operation, providing a reliable indicator of buffer busy state during swap. Cc: stable@vger.kernel.org Fixes: 4239c38fe0b3 ("ring-buffer: Process commits whenever moving to a new page.") Link: https://patch.msgid.link/20260803005640.2445666-2-wutengda@huaweicloud.com Signed-off-by: Tengda Wu Signed-off-by: Steven Rostedt --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 8e2485bb3aa8..58dc8995a88d 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6852,7 +6852,7 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, { struct ring_buffer_per_cpu *cpu_buffer_a; struct ring_buffer_per_cpu *cpu_buffer_b; - int ret = -EINVAL; + int ret = -EBUSY; if (!cpumask_test_cpu(cpu, buffer_a->cpumask) || !cpumask_test_cpu(cpu, buffer_b->cpumask)) @@ -6893,10 +6893,10 @@ int ring_buffer_swap_cpu(struct trace_buffer *buffer_a, atomic_inc(&cpu_buffer_a->record_disabled); atomic_inc(&cpu_buffer_b->record_disabled); - ret = -EBUSY; - if (local_read(&cpu_buffer_a->committing)) + /* Do not swap if either buffer is in the process of writing */ + if (cpu_buffer_a->current_context) goto out_dec; - if (local_read(&cpu_buffer_b->committing)) + if (cpu_buffer_b->current_context) goto out_dec; /* -- 2.53.0