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[34.34.182.0]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4959774736bsm9646558f8f.43.2026.11.09.01.29.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Nov 2026 01:29:49 -0800 (PST) Date: Mon, 9 Nov 2026 09:29:46 +0000 From: Vincent Donnefort To: Christian Aurich Zanettini Martins Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Sebastian Andrzej Siewior , Thomas Gleixner , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+fbe07bcf949966f3c00f@syzkaller.appspotmail.com Subject: Re: [PATCH] ring-buffer: Do not WARN when trace_rb_cpu_prepare() fails to allocate Message-ID: References: <20261104222558.863948-1-christian.aurichzm@gmail.com> 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261104222558.863948-1-christian.aurichzm@gmail.com> On Wed, Nov 04, 2026 at 07:25:58PM -0300, Christian Aurich Zanettini Martins wrote: > 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 > --- I do not believe Steven is keen on this change [1] [1] https://lore.kernel.org/all/20260806174638.6012fa24@gandalf.local.home/ > > 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 > -- Vincent