On 17.08.24 08:24, Barry Song wrote:
From: Barry Song <v-songbaohua@xxxxxxxx>
When users allocate memory with the __GFP_NOFAIL flag, they might
incorrectly use it alongside GFP_ATOMIC, GFP_NOWAIT, etc. This kind of
non-blockable __GFP_NOFAIL is not supported and is pointless. If we
attempt and still fail to allocate memory for these users, we have two
choices:
1. We could busy-loop and hope that some other direct reclamation or
kswapd rescues the current process. However, this is unreliable
and could ultimately lead to hard or soft lockups, which might not
be well supported by some architectures.
2. We could use BUG_ON to trigger a reliable system crash, avoiding
exposing NULL dereference.
Neither option is ideal, but both are improvements over the existing code.
This patch selects the second option because, with the introduction of
scoped API and GFP_NOFAIL—capable of enforcing direct reclamation for
nofail users(which is in my plan), non-blockable nofail allocations will
no longer be possible.
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: "Eugenio Pérez" <eperezma@xxxxxxxxxx>
Cc: Hailong.Liu <hailong.liu@xxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
Cc: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d2c37f8f8d09..fb5850ecd3ae 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4399,11 +4399,11 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
*/
if (gfp_mask & __GFP_NOFAIL) {
/*
- * All existing users of the __GFP_NOFAIL are blockable, so warn
- * of any new users that actually require GFP_NOWAIT
+ * All existing users of the __GFP_NOFAIL are blockable
+ * otherwise we introduce a busy loop with inside the page
+ * allocator from non-sleepable contexts
*/
- if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))
- goto fail;
+ BUG_ON(!can_direct_reclaim);
No new BUG_ON(), WARN_ON_ONCE() is good enough for something that should
be found during ordinary testing.
--
Cheers,
David / dhildenb
