linux-kernel - [PATCH] ftrace: Fix missing synchronize_rcu() removing trampoline from kallsyms

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Date:   Tue,  1 Sep 2020 12:16:17 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     peterz@...radead.org, rostedt@...dmis.org
Cc:     mingo@...hat.com, mhiramat@...nel.org, mbenes@...e.cz,
        linux-kernel@...r.kernel.org
Subject: [PATCH] ftrace: Fix missing synchronize_rcu() removing trampoline from kallsyms

Add synchronize_rcu() after list_del_rcu() in
ftrace_remove_trampoline_from_kallsyms() to protect readers of
ftrace_ops_trampoline_list (in ftrace_get_trampoline_kallsym)
which is used when kallsyms is read.

Fixes: fc0ea795f53c8d ("ftrace: Add symbols for ftrace trampolines")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 kernel/trace/ftrace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 275441254bb5..4e64367c9774 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2782,6 +2782,7 @@ static void ftrace_remove_trampoline_from_kallsyms(struct ftrace_ops *ops)
 {
 	lockdep_assert_held(&ftrace_lock);
 	list_del_rcu(&ops->list);
+	synchronize_rcu();
 }
 
 /*
-- 
2.17.1