Commit 253a0fb4 authored by Valentin Schneider's avatar Valentin Schneider Committed by Peter Zijlstra
Browse files

smp: reword smp call IPI comment 



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

  6897fc22 ("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: default avatarValentin Schneider <vschneid@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230307143558.294354-7-vschneid@redhat.com
parent 4c8c3c7f

kernel/smp.c

+4 −3
Original line number Diff line number Diff line
@@ -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