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 5CC4C194124; Thu, 21 Aug 2025 02:11:34 +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=1755742297; cv=none; b=moZ4BNU3mx65KA39UFc4ud+uFEAVDCm+53rNMbCiAhk+247lwXPRtAxP+HldKzUQl4O+hAln7YVEQnR6g/6UyuwHQTVhtBoinJXYk3GnuXmnEylpdCdVXr1KG6eYpxuVg2Bc/NWhR8cmVK6h5rvyDA+MN2n+C2VpKTGjD0M6oHs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755742297; c=relaxed/simple; bh=KfoDvDxYcogeLGEPuoMCFKFWUu0e1tr8+QbKzrTi+Ug=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=K8w2VdgIZuXf9WMcoVxaPsTZO+5saA39GHnhUz8f+9EyqQhC7aKTt7OBhgvzsSHCyP9N4gIRCsHffU3wTCOz9KxOCyUWP0m2gt33c03Hxi0hA9eWeMzkdccJo05s+9yGDtmsgFnrVrIiarrwlkI7BkUE4lEGnWBQm+8AMiXzlUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=none 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=none smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.235]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4c6myq4cxKzKHMhh; Thu, 21 Aug 2025 10:11:31 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 1C4841A0AD8; Thu, 21 Aug 2025 10:11:31 +0800 (CST) Received: from huawei.com (unknown [10.67.174.45]) by APP4 (Coremail) with SMTP id gCh0CgB38hJLgKZo7P6NEQ--.63669S2; Thu, 21 Aug 2025 10:11:30 +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 v2] ftrace: Fix potential warning in trace_printk_seq during ftrace_dump Date: Thu, 21 Aug 2025 02:11:20 +0000 Message-Id: <20250821021120.2986553-1-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:gCh0CgB38hJLgKZo7P6NEQ--.63669S2 X-Coremail-Antispam: 1UD129KBjvJXoW7Kw13WFy7Kw4fJFyDCFyfJFb_yoW8Kr1rpF y3K3srJrs5AFsrtF1UuF4xCr1xX3y0gry7WrsrJw1rJan8Ar1jvrnrt3ZaqFyfA3yDW3sI yrWYy348Cw129FJanT9S1TB71UUUUUDqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkC14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7CjxVAaw2AFwI0_ Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67 AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIY rxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14 v26r1j6r4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWUJVW8 JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjfUonmRUU 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. Fixes: d769041f8653 ("ring_buffer: implement new locking") Signed-off-by: Tengda Wu --- kernel/trace/trace.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 4283ed4e8f59..b4cec22753ea 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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