From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (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 E3BAF13C816; Wed, 20 Aug 2025 09:00:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755680434; cv=none; b=K2w3AMfamq1pJ5Wp3SEJrWIfhxKVPSV+LqCYPPBbXYyrlDbf1mjwFvg0+5xQc3kUey/RdXGjcClvOf3vQ/8U4qkcGplYEgc71Ca22Y9ZuaPSM+TyXtoXJlDew4n0r04+W26TPWYFzG61gCqvJ3ft5XIo3U646DFd2ibany6n5/M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755680434; c=relaxed/simple; bh=R3yfDPxehjuYfsd99Fu7QrZq0lSS2Wlmj1idbjeLmYU=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=dgrOD/Pz/WR48FE/dqzcaubswC4Uh82Dw0yOsaJnsowSiPACqO6Nwz2WqgOKC5HsRwBVjkEARWWTwVHMHrn9LPH/Glo6h3TNquWDxMAIq+oMeY9cBEi7eb2V8G+tF0tkUAV9DtgMCb7n3FuzXsnA0lXsNnOYxBrCa24Me/jMUWU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4c6L583Ss7zKHNpK; Wed, 20 Aug 2025 17:00:28 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id E64111A0CE7; Wed, 20 Aug 2025 17:00:27 +0800 (CST) Received: from huawei.com (unknown [10.67.174.45]) by APP4 (Coremail) with SMTP id gCh0CgCHURKkjqVonnY8EQ--.11889S2; Wed, 20 Aug 2025 17:00:27 +0800 (CST) From: Tengda Wu To: Steven Rostedt , Masami Hiramatsu Cc: Mark Rutland , Mathieu Desnoyers , Ingo Molnar , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, Tengda Wu Subject: [PATCH -next] ftrace: Fix potential warning in trace_printk_seq during ftrace_dump Date: Wed, 20 Aug 2025 09:00:17 +0000 Message-Id: <20250820090017.2978279-1-wutengda@huaweicloud.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgCHURKkjqVonnY8EQ--.11889S2 X-Coremail-Antispam: 1UD129KBjvJXoWxJFykArW8Ar18tF1ktFW8WFg_yoW5AF1UpF 9xK3srJr4kAFsrtFn8uF4xGw1xJay0qry7WrsrJw1rAan8Ar4j9rnxtwnaqFyfC398G3sI yFWjy3yDCw129FJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkC14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7CjxVAaw2AFwI0_ JF0_Jw1l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67 AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIY rxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14 v26r1j6r4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8 JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjfUYCJmUU UUU X-CM-SenderInfo: pzxwv0hjgdqx5xdzvxpfor3voofrz/ 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. The issue occurs because: CPU0 (ftrace_dump) CPU1 (reader) echo z > /proc/sysrq-trigger !trace_empty(&iter) trace_iterator_reset(&iter) <- len = size = 0 cat /sys/kernel/tracing/trace_pipe trace_find_next_entry_inc(&iter) __find_next_entry ring_buffer_empty_cpu <- all empty return NULL trace_printk_seq(&iter.seq) WARN_ON_ONCE(s->seq.len >= s->seq.size) 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 populate `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. Add a non-NULL check on the return value of trace_find_next_entry_inc prior to invoking trace_printk_seq, ensuring the `iter.seq` is properly populated before subsequent operations. Furthermore, per the seq_buf specification, the condition len == size indicates a full buffer, which constitutes a valid state. Consequently, the equality check and size - 1 adjustment in WARN_ON_ONCE() are redundant and should be eliminated. Fixes: d769041f8653 ("ring_buffer: implement new locking") Signed-off-by: Tengda Wu --- kernel/trace/trace.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 4283ed4e8f59..61c5d389dbd3 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -10521,8 +10521,8 @@ trace_printk_seq(struct trace_seq *s) * PAGE_SIZE, and TRACE_MAX_PRINT is 1000, this is just * an extra layer of protection. */ - if (WARN_ON_ONCE(s->seq.len >= s->seq.size)) - s->seq.len = s->seq.size - 1; + if (WARN_ON_ONCE(s->seq.len > s->seq.size)) + s->seq.len = s->seq.size; /* should be zero ended, but we are paranoid. */ s->buffer[s->seq.len] = 0; @@ -10617,6 +10617,7 @@ static void ftrace_dump_one(struct trace_array *tr, enum ftrace_dump_mode dump_m */ while (!trace_empty(&iter)) { + void *ent; if (!cnt) printk(KERN_TRACE "---------------------------------\n"); @@ -10625,17 +10626,18 @@ static void ftrace_dump_one(struct trace_array *tr, enum ftrace_dump_mode dump_m trace_iterator_reset(&iter); iter.iter_flags |= TRACE_FILE_LAT_FMT; + ent = trace_find_next_entry_inc(&iter); - if (trace_find_next_entry_inc(&iter) != NULL) { + if (ent) { int ret; ret = print_trace_line(&iter); if (ret != TRACE_TYPE_NO_CONSUME) trace_consume(&iter); + + trace_printk_seq(&iter.seq); } touch_nmi_watchdog(); - - trace_printk_seq(&iter.seq); } if (!cnt) -- 2.34.1