[PATCH v10 08/14] smp: Remove preempt_disable() from on_each_cpu_cond_mask()

[Chuyi Zhou]

smp_call_function_many_cond() handles the preemption and CPU pinning
requirements internally. on_each_cpu_cond_mask() only builds the call
flags and forwards the request to that helper.

Remove the outer preempt_disable() and preempt_enable() pair from
on_each_cpu_cond_mask().

Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 kernel/smp.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index 5226f6879561..de04335524d8 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -1114,12 +1114,14 @@ void __init smp_init(void)
  * @func:	The function to run on all applicable CPUs.
  *		This must be fast and non-blocking.
  * @info:	An arbitrary pointer to pass to both functions.
- * @wait:	If true, wait (atomically) until function has
- *		completed on other CPUs.
+ * @wait:	If true, wait until function has completed on other CPUs.
  * @mask:	The set of cpus to run on (only runs on online subset).
  *
- * Preemption is disabled to protect against CPUs going offline but not online.
- * CPUs going online during the call will not be seen or sent an IPI.
+ * Target CPU selection and work queueing are done with preemption
+ * disabled. This protects against CPUs going offline, but not against
+ * CPUs coming online concurrently; newly online CPUs are not guaranteed
+ * to be seen or sent an IPI. If @wait is true, the final wait for remote
+ * completion happens after that preemption-disabled section.
  *
  * You must not call this function with disabled interrupts or
  * from a hardware interrupt handler or from a bottom half handler.
@@ -1132,9 +1134,7 @@ void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
 	if (wait)
 		scf_flags |= SCF_WAIT;
 
-	preempt_disable();
 	smp_call_function_many_cond(mask, func, info, scf_flags, cond_func);
-	preempt_enable();
 }
 EXPORT_SYMBOL(on_each_cpu_cond_mask);
 
-- 
2.20.1