smp: reword smp call IPI comment

Accessing the call_single_queue hasn't involved a spinlock since 2014:

  6897fc22ea01 ("kernel: use lockless list for smp_call_function_single")

The llist operations (namely cmpxchg() and xchg()) provide similar ordering
guarantees, update the comment to lessen confusion.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230307143558.294354-7-vschneid@redhat.com

diff --git a/kernel/smp.c b/kernel/smp.c
index 03e6d576295de5d9299e5e0212ff0a72b68934d6..6bbfabbe62fc2772bf8f883e02513ffe9690e704 100644 (file)
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -312,9 +312,10 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
 void __smp_call_single_queue(int cpu, struct llist_node *node)
 {
        /*
-        * The list addition should be visible before sending the IPI
-        * handler locks the list to pull the entry off it because of
-        * normal cache coherency rules implied by spinlocks.
+        * The list addition should be visible to the target CPU when it pops
+        * the head of the list to pull the entry off it in the IPI handler
+        * because of normal cache coherency rules implied by the underlying
+        * llist ops.
         *
         * If IPIs can go out of order to the cache coherency protocol
         * in an architecture, sufficient synchronisation should be added