ftrace: Add comment to why rcu_dereference_sched() is open coded
authorSteven Rostedt (VMware) <rostedt@goodmis.org>
Wed, 5 Feb 2020 07:17:57 +0000 (02:17 -0500)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Tue, 11 Feb 2020 12:34:04 +0000 (04:34 -0800)
commitc03d23598062175c450a646763c2c0045a7aa35e
treea67820ecaea2599f0c99ebfbf34b95592227f065
parent30afa80b0f6e03134d8e7d66a1111d066403ad3f
ftrace: Add comment to why rcu_dereference_sched() is open coded

[ Upstream commit 16052dd5bdfa16dbe18d8c1d4cde2ddab9d23177 ]

Because the function graph tracer can execute in sections where RCU is not
"watching", the rcu_dereference_sched() for the has needs to be open coded.
This is fine because the RCU "flavor" of the ftrace hash is protected by
its own RCU handling (it does its own little synchronization on every CPU
and does not rely on RCU sched).

Acked-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
kernel/trace/trace.h