mm: kvmalloc does not fallback to vmalloc for incompatible gfp flags

kvmalloc warned about incompatible gfp_mask to catch abusers (mostly GFP_NOFS) with an intention that this will motivate authors of the code to fix those. Linus argues that this just motivates people to do even more hacks like if (gfp == GFP_KERNEL) kvmalloc else kmalloc I haven't seen this happening much (Linus pointed to bucket_lock special cases an atomic allocation but my git foo hasn't found much more) but it is true that we can grow those in future. Therefore Linus suggested to simply not fallback to vmalloc for incompatible gfp flags and rather stick with the kmalloc path. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Michal Hocko <[email protected]> Suggested-by: Linus Torvalds <[email protected]> Cc: Tom Herbert <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
olifre · Jun 8, 2018 · ce91f6e · ce91f6e
1 parent 4b33b69
commit ce91f6e
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Showing 2 changed files with 5 additions and 6 deletions.
diff --git a/lib/bucket_locks.c b/lib/bucket_locks.c
@@ -30,10 +30,7 @@ int alloc_bucket_spinlocks(spinlock_t **locks, unsigned int *locks_mask,
 	}
 
 	if (sizeof(spinlock_t) != 0) {
-		if (gfpflags_allow_blocking(gfp))
-			tlocks = kvmalloc(size * sizeof(spinlock_t), gfp);
-		else
-			tlocks = kmalloc_array(size, sizeof(spinlock_t), gfp);
+		tlocks = kvmalloc_array(size, sizeof(spinlock_t), gfp);
 		if (!tlocks)
 			return -ENOMEM;
 		for (i = 0; i < size; i++)

diff --git a/mm/util.c b/mm/util.c
@@ -391,7 +391,8 @@ EXPORT_SYMBOL(vm_mmap);
  * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is
  * preferable to the vmalloc fallback, due to visible performance drawbacks.
  *
- * Any use of gfp flags outside of GFP_KERNEL should be consulted with mm people.
+ * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not
+ * fall back to vmalloc.
  */
 void *kvmalloc_node(size_t size, gfp_t flags, int node)
 {
@@ -402,7 +403,8 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
 	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
 	 * so the given set of flags has to be compatible.
 	 */
-	WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
+	if ((flags & GFP_KERNEL) != GFP_KERNEL)
+		return kmalloc_node(size, flags, node);
 
 	/*
 	 * We want to attempt a large physically contiguous block first because