From nobody Fri Oct 3 23:02:07 2025 Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) (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 EEDFE25B1D3 for ; Fri, 22 Aug 2025 16:11:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.10 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755879103; cv=none; b=jSzO1lSwjGCY/5YLQHXS+BA12cROMLpjYOEcdw6NmzSPj0UeMI7706p7ONy/pFHbm2e7AocTd0DS2qG1zERW4YqPYNegC/EtQ5SyFy2PKTww/BPZCr4RD2gdBN1Ihcpj0eSQ5Cb6XglC8OUd7IulgaANxioc/PguOH3prgoX4so= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755879103; c=relaxed/simple; bh=VyZ48+G6VgzVZAypOE6VLo9sOSiHOXzmB0kFglnpo2E=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type; b=AbfmZkJQTCXDKrwb69OVvX3Y17HkTaDSZS4KijLQy1Ng3CB1MjHmsnbneEMuc+o0+yk80+lWgiK0KJoeL+hMegz3GwE2ob0KadTLrfofpuReYHR+ST8yOY6bbWh2DA3ESXpbNdFVGOjmRF6LRhr3xEbZuGxpuWwAv5CdLMJXj7c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf11.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 88332B79D4; Fri, 22 Aug 2025 16:11:33 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf11.hostedemail.com (Postfix) with ESMTPA id C9B3920031; Fri, 22 Aug 2025 16:11:31 +0000 (UTC) Date: Fri, 22 Aug 2025 12:11:38 -0400 From: Steven Rostedt To: LKML Cc: Masami Hiramatsu , Mathieu Desnoyers , Tengda Wu Subject: [for-linus][PATCH] ftrace: Fix potential warning in trace_printk_seq during ftrace_dump Message-ID: <20250822121138.5e113885@gandalf.local.home> X-Mailer: Claws Mail 3.20.0git84 (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-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C9B3920031 X-Stat-Signature: aey9gru6jmphu1sd1acbu4jxkzbkhi9z X-Rspamd-Server: rspamout06 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX198ymj7XOI74WWnU2Q7uO7tJ5j3zr8/57E= X-HE-Tag: 1755879091-964502 X-HE-Meta: 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 Content-Type: text/plain; charset="utf-8" git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git trace/fixes Head SHA1: c1e730442be2902ad5f9acc244ffc6e6400b981a Tengda Wu (1): ftrace: Fix potential warning in trace_printk_seq during ftrace_dump ---- kernel/trace/trace.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --------------------------- commit c1e730442be2902ad5f9acc244ffc6e6400b981a Author: Tengda Wu Date: Fri Aug 22 03:33:43 2025 +0000 ftrace: Fix potential warning in trace_printk_seq during ftrace_dump =20 When calling ftrace_dump_one() concurrently with reading trace_pipe, a WARN_ON_ONCE() in trace_printk_seq() can be triggered due to a race condition. =20 The issue occurs because: =20 CPU0 (ftrace_dump) CPU1 (reader) echo z > /proc/sysrq-trigger =20 !trace_empty(&iter) trace_iterator_reset(&iter) <- len =3D size =3D 0 cat /sys/kernel/tracing= /trace_pipe trace_find_next_entry_inc(&iter) __find_next_entry ring_buffer_empty_cpu <- all empty return NULL =20 trace_printk_seq(&iter.seq) WARN_ON_ONCE(s->seq.len >=3D s->seq.size) =20 In the context between trace_empty() and trace_find_next_entry_inc() during ftrace_dump, the ring buffer data was consumed by other readers. This caused trace_find_next_entry_inc to return NULL, failing to popula= te `iter.seq`. At this point, due to the prior trace_iterator_reset, both `iter.seq.len` and `iter.seq.size` were set to 0. Since they are equal, the WARN_ON_ONCE condition is triggered. =20 Move the trace_printk_seq() into the if block that checks to make sure = the return value of trace_find_next_entry_inc() is non-NULL in ftrace_dump_one(), ensuring the 'iter.seq' is properly populated before subsequent operations. =20 Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Ingo Molnar Link: https://lore.kernel.org/20250822033343.3000289-1-wutengda@huaweic= loud.com Fixes: d769041f8653 ("ring_buffer: implement new locking") Signed-off-by: Tengda Wu Signed-off-by: Steven Rostedt (Google) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 8d8935ed416d..1b7db732c0b1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -10638,10 +10638,10 @@ static void ftrace_dump_one(struct trace_array *t= r, enum ftrace_dump_mode dump_m ret =3D print_trace_line(&iter); if (ret !=3D TRACE_TYPE_NO_CONSUME) trace_consume(&iter); + + trace_printk_seq(&iter.seq); } touch_nmi_watchdog(); - - trace_printk_seq(&iter.seq); } =20 if (!cnt)