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: Barry Song <v-songbaohua@oppo.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal 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: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/gfp_types.h b/include/linux/gfp_types.h
index 4a1fa7706b0c0cee337482bacaa21ce3a7f42e45..65db9349f9053c701e24bdcf1dfe6afbf1278a2d 100644 (file)
--- a/include/linux/gfp_types.h
+++ b/include/linux/gfp_types.h
@@ -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)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3469ca78bf7a2589c7a6a04bae1388acf5880330..23509b823e2ba6a58909b8b43ad4c6138ab125a1 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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 @@ nopage:
         * 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