preempt_enable_no_resched() was used based on review feedback that had no strong objection at the time. The thinking was that it avoided adding a preemption point where one didn't exist before so the feedback was applied. This reasoning was wrong. There was an indirect preemption point as explained by Thomas Gleixner where an interrupt could set_need_resched() followed by preempt_enable being a preemption point that matters. This use of preempt_enable_no_resched is bad from both a mainline and RT perspective and a violation of the preemption mechanism. Peter Zijlstra noted that "the only acceptable use of preempt_enable_no_resched() is if the next statement is a schedule() variant". The usage was outright broken and I should have stuck to preempt_enable() as it was originally developed. It's known from previous tests that there was no detectable difference to the performance by using preempt_enable_no_resched(). This is a fix to the mmotm patch mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index eaecb4b145e6..2a36dad03dac 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2520,7 +2520,7 @@ void free_hot_cold_page(struct page *page, bool cold) } out: - preempt_enable_no_resched(); + preempt_enable(); } /* @@ -2686,7 +2686,7 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, __count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order); zone_statistics(preferred_zone, zone); } - preempt_enable_no_resched(); + preempt_enable(); return page; } -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
