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 2BE2C45DF6B; Fri, 7 Aug 2026 22:17:12 +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=1786141034; cv=none; b=poTa0WZnf+8hEjZBeOhDQdgwASuYwQ30nOxI+BnGOULUaypTOplQ3hodgktK8SUuzO7VUJJxaghNNO1zo2Foj8Ae6/CD/Nc09dTV4Mq9UFBZw/rjdHJKFeei/sj+F3BNB1uOhqQk4/+u7uGGT8j/XQGsHV9iCKrNdAipjfVUrlc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786141034; c=relaxed/simple; bh=3ARzX+XpBlfGQj3hEMHI8qeJiUjDkqFuFKZt1QU065U=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=Pvqm/6kKBvfaV0CQwPwCStrsHlwpuhWgQ6AxUEAXX/igfe/smpcjipUcUR3PJ8bAWLx8IVuHrgz5p9/w1QgHVJncwVA/5ZyyawSbNxF5P8RAOqWe1zRAGLWbNfM5lHTahxKBCIyp2t5vni5605FrRDPxTVDDbDjGhosFIzoatMU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e8IUx32c; 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="e8IUx32c" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E4D4E1F000E9; Fri, 7 Aug 2026 22:17:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786141032; bh=xxrPQ3n/bRUMadST9eYFb+N+ZW6gaQSsn/Y02AdyFf0=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=e8IUx32ckAliPJvX3zMfqn4f/MS/q6TDFnMuEQeL7czl+DY2+KOCkX69LJDhjLEK+ fLnrVBfgnScLkjOAnO1SDWOTJoOgbVihiphMhh0TmXGZXKAVi6MDv+vml8h2EzQe/I X2QpifqoBRKk8VkRcaPex9ZgSo48zrhCn5puYYuGfXJYwQbc+w23+LJYYiwRyDuSqS DoKVd9XXosngCcmYnPzc5kf6dgIB36Z2rVbfao2OVX8m5NFPUCUNI8aQJ92WLM1p/l VzlM8WwH/4YCknIXzNsmeU2BndUPvJGazK3CpBVriNRk8k2a8WmiEgYmXjmfB2ZZPW eerj6YbTug+7A== Date: Sat, 8 Aug 2026 07:17:08 +0900 From: Masami Hiramatsu (Google) To: Hui Su Cc: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH] ring-buffer: Fix crash passing ERR_PTR to kthread_stop() Message-Id: <20260808071708.6bcbac3a30c5a58fa1a4c2b0@kernel.org> In-Reply-To: <20260807154145.2846521-2-sh_def@163.com> References: <20260807154145.2846521-2-sh_def@163.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 7 Aug 2026 23:41:46 +0800 Hui Su wrote: > In test_ringbuffer()'s out_free cleanup loop, the check > `!rb_threads[cpu]` only catches NULL entries and misses entries that > hold an ERR_PTR. > > rb_threads[] is static, so unassigned slots are NULL. But when > kthread_run_on_cpu() fails for a cpu, it stores ERR_PTR(-ENOMEM) (or > -EINTR) in rb_threads[cpu] before the creation loop jumps to out_free. > That entry is non-NULL, so the old `!ptr` check does not break, and the > cleanup proceeds to call kthread_stop() on the ERR_PTR. kthread_stop() > then dereferences the bogus pointer, crashing the kernel during the > late_initcall self-test. > > crash logs: > BUG: kernel NULL pointer dereference, address: 000000000000001c > Oops: 0002 [#1] SMP NOPTI > CPU: 1 PID: 1 Comm: swapper/0 Not tainted 7.2.0-rc6-dirty #7 PREEMPT(lazy) > RIP: 0010:kthread_stop+0x2e/0x220 > RBX: fffffffffffffff4 > CR2: 000000000000001c > Call Trace: > > test_ringbuffer+0x1ec/0x650 > do_one_initcall+0x6c/0x2c0 > kernel_init_freeable+0x21d/0x420 > kernel_init+0x15/0x1c0 > ret_from_fork+0x21b/0x320 > > Kernel panic - not syncing: Fatal exception > > Fixes: 64ed3a049e3e ("ring-buffer: make use of the helper function kthread_run_on_cpu()") > Signed-off-by: Hui Su Look good to me. Acked-by: Masami Hiramatsu (Google) Thank you! > --- > kernel/trace/ring_buffer.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 8e2485bb3aa8..6af7e36ca526 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -8214,7 +8214,7 @@ static __init int test_ringbuffer(void) > > out_free: > for_each_online_cpu(cpu) { > - if (!rb_threads[cpu]) > + if (IS_ERR_OR_NULL(rb_threads[cpu])) > break; > kthread_stop(rb_threads[cpu]); > } > -- > 2.43.0 > -- Masami Hiramatsu (Google)