Commit 4230e2de authored Oct 21, 2020 by Zong Li Committed by Thomas Gleixner Oct 26, 2020

stop_machine, rcu: Mark functions as notrace



Some architectures assume that the stopped CPUs don't make function calls
to traceable functions when they are in the stopped state. See also commit
cb9d7fd5 ("watchdog: Mark watchdog touch functions as notrace").

Violating this assumption causes kernel crashes when switching tracer on
RISC-V.

Mark rcu_momentary_dyntick_idle() and stop_machine_yield() notrace to
prevent this.

Fixes: 4ecf0a43 ("processor: get rid of cpu_relax_yield")
Fixes: 366237e7 ("stop_machine: Provide RCU quiescent state in multi_cpu_stop()")
Signed-off-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Atish Patra <atish.patra@wdc.com>
Tested-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201021073839.43935-1-zong.li@sifive.com

parent 3650b228

kernel/rcu/tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -409,7 +409,7 @@ bool rcu_eqs_special_set(int cpu)
		*
		* The caller must have disabled interrupts and must not be idle.
		*/
		void rcu_momentary_dyntick_idle(void)
		notrace void rcu_momentary_dyntick_idle(void)
		{
		int special;

kernel/stop_machine.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -178,7 +178,7 @@ static void ack_state(struct multi_stop_data *msdata)
		set_state(msdata, msdata->state + 1);
		}

		void __weak stop_machine_yield(const struct cpumask *cpumask)
		notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
		{
		cpu_relax();
		}

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