mm: kvmalloc: add non-blocking support for vmalloc

Extend __kvmalloc_node_noprof() to handle non-blocking GFP flags
(GFP_NOWAIT and GFP_ATOMIC).  Previously such flags were rejected,
returning NULL.  With this change:

- kvmalloc() can fall back to vmalloc() if non-blocking contexts;
- for non-blocking allocations the VM_ALLOW_HUGE_VMAP option is
  disabled, since the huge mapping path still contains might_sleep();
- documentation update to reflect that GFP_NOWAIT and GFP_ATOMIC
  are now supported.

Link: https://lkml.kernel.org/r/20251007122035.56347-11-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Marco Elver <elver@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index f9a396cc9c09e5f1e14a08b4f40b4056676fffd5..b7442015f64047e0f7215c5dbeccb90780440363 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -7063,7 +7063,7 @@ static gfp_t kmalloc_gfp_adjust(gfp_t flags, size_t size)
  * Uses kmalloc to get the memory but if the allocation fails then falls back
  * to the vmalloc allocator. Use kvfree for freeing the memory.
  *
- * GFP_NOWAIT and GFP_ATOMIC are not supported, neither is the __GFP_NORETRY modifier.
+ * GFP_NOWAIT and GFP_ATOMIC are supported, the __GFP_NORETRY modifier is not.
  * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is
  * preferable to the vmalloc fallback, due to visible performance drawbacks.
  *
@@ -7072,6 +7072,7 @@ static gfp_t kmalloc_gfp_adjust(gfp_t flags, size_t size)
 void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), unsigned long align,
                             gfp_t flags, int node)
 {
+       bool allow_block;
        void *ret;
 
        /*
@@ -7084,16 +7085,22 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), unsigned long align,
        if (ret || size <= PAGE_SIZE)
                return ret;
 
-       /* non-sleeping allocations are not supported by vmalloc */
-       if (!gfpflags_allow_blocking(flags))
-               return NULL;
-
        /* Don't even allow crazy sizes */
        if (unlikely(size > INT_MAX)) {
                WARN_ON_ONCE(!(flags & __GFP_NOWARN));
                return NULL;
        }
 
+       /*
+        * For non-blocking the VM_ALLOW_HUGE_VMAP is not used
+        * because the huge-mapping path in vmalloc contains at
+        * least one might_sleep() call.
+        *
+        * TODO: Revise huge-mapping path to support non-blocking
+        * flags.
+        */
+       allow_block = gfpflags_allow_blocking(flags);
+
        /*
         * kvmalloc() can always use VM_ALLOW_HUGE_VMAP,
         * since the callers already cannot assume anything
@@ -7101,7 +7108,7 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), unsigned long align,
         * protection games.
         */
        return __vmalloc_node_range_noprof(size, align, VMALLOC_START, VMALLOC_END,
-                       flags, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
+                       flags, PAGE_KERNEL, allow_block ? VM_ALLOW_HUGE_VMAP:0,
                        node, __builtin_return_address(0));
 }
 EXPORT_SYMBOL(__kvmalloc_node_noprof);