Commit 903edea6 authored by Barry Song's avatar Barry Song Committed by Andrew Morton
Browse files

mm: warn about illegal __GFP_NOFAIL usage in a more appropriate location and manner 

Three points for this change:

1. We should consolidate all warnings in one place. Currently, the
   order > 1 warning is in the hotpath, while others are in less
   likely scenarios. Moving all warnings to the slowpath will reduce
   the overhead for order > 1 and increase the visibility of other
   warnings.

2. We currently have two warnings for order: one for order > 1 in
   the hotpath and another for order > costly_order in the laziest
   path. I suggest standardizing on order > 1 since it's been in
   use for a long time.

3. We don't need to check for __GFP_NOWARN in this case. __GFP_NOWARN
   is meant to suppress allocation failure reports, but here we're
   dealing with bug detection, not allocation failures. So replace
   WARN_ON_ONCE_GFP by WARN_ON_ONCE.

[v-songbaohua@oppo.com: also update the doc for __GFP_NOFAIL with order > 1]
  Link: https://lkml.kernel.org/r/20240903223935.1697-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240830202823.21478-4-21cnbao@gmail.com


Signed-off-by: default avatarBarry Song <v-songbaohua@oppo.com>
Suggested-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: David Rientjes <rientjes@google.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: Hailong.Liu <hailong.liu@oppo.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Xie Yongji <xieyongji@bytedance.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 17d75422

include/linux/gfp_types.h

+2 −1
Original line number Diff line number Diff line
@@ -253,7 +253,8 @@ enum { 
 * used only when there is no reasonable failure policy) but it is

 * definitely preferable to use the flag rather than opencode endless

 * loop around allocator.

 * Using this flag for costly allocations is _highly_ discouraged.

 * Allocating pages from the buddy with __GFP_NOFAIL and order > 1 is

 * not supported. Please consider using kvmalloc() instead.

 */

#define __GFP_IO	((__force gfp_t)___GFP_IO)

#define __GFP_FS	((__force gfp_t)___GFP_FS)

mm/page_alloc.c

+25 −25
Original line number Diff line number Diff line
@@ -3032,12 +3032,6 @@ struct page *rmqueue(struct zone *preferred_zone, 
{

	struct page *page;



	/*

	 * We most definitely don't want callers attempting to

	 * allocate greater than order-1 page units with __GFP_NOFAIL.

	 */

	WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));



	if (likely(pcp_allowed_order(order))) {

		page = rmqueue_pcplist(preferred_zone, zone, order,

				       migratetype, alloc_flags);
@@ -4175,6 +4169,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, 
{

	bool can_direct_reclaim = gfp_mask & __GFP_DIRECT_RECLAIM;

	bool can_compact = gfp_compaction_allowed(gfp_mask);

	bool nofail = gfp_mask & __GFP_NOFAIL;

	const bool costly_order = order > PAGE_ALLOC_COSTLY_ORDER;

	struct page *page = NULL;

	unsigned int alloc_flags;
@@ -4187,6 +4182,25 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, 
	unsigned int zonelist_iter_cookie;

	int reserve_flags;



	if (unlikely(nofail)) {

		/*

		 * We most definitely don't want callers attempting to

		 * allocate greater than order-1 page units with __GFP_NOFAIL.

		 */

		WARN_ON_ONCE(order > 1);

		/*

		 * Also we don't support __GFP_NOFAIL without __GFP_DIRECT_RECLAIM,

		 * otherwise, we may result in lockup.

		 */

		WARN_ON_ONCE(!can_direct_reclaim);

		/*

		 * PF_MEMALLOC request from this context is rather bizarre

		 * because we cannot reclaim anything and only can loop waiting

		 * for somebody to do a work for us.

		 */

		WARN_ON_ONCE(current->flags & PF_MEMALLOC);

	}



restart:

	compaction_retries = 0;

	no_progress_loops = 0;
@@ -4404,29 +4418,15 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, 
	 * Make sure that __GFP_NOFAIL request doesn't leak out and make sure

	 * we always retry

	 */

	if (gfp_mask & __GFP_NOFAIL) {

	if (unlikely(nofail)) {

		/*

		 * All existing users of the __GFP_NOFAIL are blockable, so warn

		 * of any new users that actually require GFP_NOWAIT

		 * Lacking direct_reclaim we can't do anything to reclaim memory,

		 * we disregard these unreasonable nofail requests and still

		 * return NULL

		 */

		if (WARN_ON_ONCE_GFP(!can_direct_reclaim, gfp_mask))

		if (!can_direct_reclaim)

			goto fail;



		/*

		 * PF_MEMALLOC request from this context is rather bizarre

		 * because we cannot reclaim anything and only can loop waiting

		 * for somebody to do a work for us

		 */

		WARN_ON_ONCE_GFP(current->flags & PF_MEMALLOC, gfp_mask);



		/*

		 * non failing costly orders are a hard requirement which we

		 * are not prepared for much so let's warn about these users

		 * so that we can identify them and convert them to something

		 * else.

		 */

		WARN_ON_ONCE_GFP(costly_order, gfp_mask);



		/*

		 * Help non-failing allocations by giving some access to memory

		 * reserves normally used for high priority non-blocking