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Wed, 04 Nov 2026 14:26:31 -0800 (PST) Received: from bridge.vpn.bridge.ufsc.br ([2804:14d:ba6b:8339:9401:67ca:4be7:55d0]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5eca89b6568sm2863977e0c.1.2026.11.04.14.26.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 14:26:30 -0800 (PST) From: Christian Aurich Zanettini Martins To: Steven Rostedt Cc: Masami Hiramatsu , Mathieu Desnoyers , Vincent Donnefort , Sebastian Andrzej Siewior , Thomas Gleixner , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Christian Aurich Zanettini Martins , syzbot+fbe07bcf949966f3c00f@syzkaller.appspotmail.com Subject: [PATCH] ring-buffer: Do not WARN when trace_rb_cpu_prepare() fails to allocate Date: Wed, 4 Nov 2026 19:25:58 -0300 Message-ID: <20261104222558.863948-1-christian.aurichzm@gmail.com> X-Mailer: git-send-email 2.43.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Creating a tracing instance allocates the buffers of the other CPUs through trace_rb_cpu_prepare(), which WARNs if the allocation fails. But __rb_allocate_pages() bails out on purpose when si_mem_available() is too low or the task gets killed, so a mkdir in instances/ with a large trace_buf_size is enough to trigger it: WARNING: kernel/trace/ring_buffer.c:8094 at trace_rb_cpu_prepare+0xf1/0x100 The same failure for the current CPU, or in ring_buffer_resize(), just returns -ENOMEM. Use pr_warn() here instead. Fixes: b32614c03413 ("tracing/rb: Convert to hotplug state machine") Reported-by: syzbot+fbe07bcf949966f3c00f@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6a707c4f.13bfb6d0.1ecdd5.027e.GAE@google.com/ Signed-off-by: Christian Aurich Zanettini Martins --- Notes: Tested in QEMU on 05441d697f7f (4 CPUs, 1G, trace_buf_size=350M): mkdir in instances/ WARNs every time before and only prints the message after. Same with a mkdir killed during the allocation. kernel/trace/ring_buffer.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 1fd28a72e6ee..c018559ad61a 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -8091,8 +8091,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node) buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { - WARN(1, "failed to allocate ring buffer on CPU %u\n", - cpu); + pr_warn("failed to allocate ring buffer on CPU %u\n", cpu); return -ENOMEM; } -- 2.43.0