page-allocator: warn if __GFP_NOFAIL is used for a large allocation

__GFP_NOFAIL is a bad fiction.  Allocations _can_ fail, and callers should
detect and suitably handle this (and not by lamely moving the infinite
loop up to the caller level either).

Attempting to use __GFP_NOFAIL for a higher-order allocation is even
worse, so add a once-off runtime check for this to slap people around for
even thinking about trying it.

Cc: David Rientjes <rientjes@google.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 076463cb21b..61290ea721c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1128,6 +1128,19 @@ again:
                 list_del(&page->lru);
                 pcp->count--;
         } else {
+                if (unlikely(gfp_flags & __GFP_NOFAIL)) {
+                        /*
+                         * __GFP_NOFAIL is not to be used in new code.
+                         *
+                         * All __GFP_NOFAIL callers should be fixed so that they
+                         * properly detect and handle allocation failures.
+                         *
+                         * We most definitely don't want callers attempting to
+                         * allocate greater than single-page units with
+                         * __GFP_NOFAIL.
+                         */
+                        WARN_ON_ONCE(order > 0);
+                }
                 spin_lock_irqsave(&zone->lock, flags);
                 page = __rmqueue(zone, order, migratetype);
                 __mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << order));