linux-kernel - [for-linus][PATCH 5/6] trace/fgraph: Fix the warning caused by missing unregister notifier

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Message-ID: <20250821000014.982314449@kernel.org>
Date: Wed, 20 Aug 2025 20:00:05 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Ye Weihua <yeweihua4@...wei.com>
Subject: [for-linus][PATCH 5/6] trace/fgraph: Fix the warning caused by missing unregister notifier

From: Ye Weihua <yeweihua4@...wei.com>

This warning was triggered during testing on v6.16:

notifier callback ftrace_suspend_notifier_call already registered
WARNING: CPU: 2 PID: 86 at kernel/notifier.c:23 notifier_chain_register+0x44/0xb0
...
Call Trace:
 <TASK>
 blocking_notifier_chain_register+0x34/0x60
 register_ftrace_graph+0x330/0x410
 ftrace_profile_write+0x1e9/0x340
 vfs_write+0xf8/0x420
 ? filp_flush+0x8a/0xa0
 ? filp_close+0x1f/0x30
 ? do_dup2+0xaf/0x160
 ksys_write+0x65/0xe0
 do_syscall_64+0xa4/0x260
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

When writing to the function_profile_enabled interface, the notifier was
not unregistered after start_graph_tracing failed, causing a warning the
next time function_profile_enabled was written.

Fixed by adding unregister_pm_notifier in the exception path.

Link: https://lore.kernel.org/20250818073332.3890629-1-yeweihua4@huawei.com
Fixes: 4a2b8dda3f870 ("tracing/function-graph-tracer: fix a regression while suspend to disk")
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Ye Weihua <yeweihua4@...wei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 kernel/trace/fgraph.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index f4d200f0c610..2a42c1036ea8 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1397,6 +1397,7 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 		ftrace_graph_active--;
 		gops->saved_func = NULL;
 		fgraph_lru_release_index(i);
+		unregister_pm_notifier(&ftrace_suspend_notifier);
 	}
 	return ret;
 }
-- 
2.50.1