It's reasonable for users of on_cpu() and on_cpumask() to assume
they can read data that 'func' has written when the call completes.
Ensure the caller doesn't observe a completion (target cpus are again
idle) without also being able to observe any writes which were made
by func(). Do so by adding barriers to implement the following
target-cpu calling-cpu
---------- -----------
func() /* store something */ /* wait for target to be idle */
smp_wmb(); smp_rmb();
set_cpu_idle(smp_processor_id(), true); /* load what func() stored */
Signed-off-by: Andrew Jones <andrew.jones@xxxxxxxxx>
---
lib/on-cpus.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/lib/on-cpus.c b/lib/on-cpus.c
index f6072117fa1b..356f284be61b 100644
--- a/lib/on-cpus.c
+++ b/lib/on-cpus.c
@@ -79,6 +79,7 @@ void do_idle(void)
smp_wait_for_event();
smp_rmb();
on_cpu_info[cpu].func(on_cpu_info[cpu].data);
+ smp_wmb(); /* pairs with the smp_rmb() in on_cpu() and on_cpumask() */
}
}
@@ -145,12 +146,14 @@ void on_cpumask(const cpumask_t *mask, void (*func)(void *data), void *data)
smp_wait_for_event();
for_each_cpu(cpu, mask)
cpumask_clear_cpu(me, &on_cpu_info[cpu].waiters);
+ smp_rmb(); /* pairs with the smp_wmb() in do_idle() */
}
void on_cpu(int cpu, void (*func)(void *data), void *data)
{
on_cpu_async(cpu, func, data);
cpu_wait(cpu);
+ smp_rmb(); /* pairs with the smp_wmb() in do_idle() */
}
void on_cpus(void (*func)(void *data), void *data)
--
2.47.0
