objpool: fix to make percpu slot allocation more robust

Since gfp & GFP_ATOMIC == GFP_ATOMIC is true for GFP_KERNEL | GFP_HIGH, it
will use kmalloc if user specifies that combination.  Here the reason why
combining the __vmalloc_node() and kmalloc_node() is that the vmalloc does
not support all GFP flag, especially GFP_ATOMIC.  So we should check if
gfp & (GFP_ATOMIC | GFP_KERNEL) != GFP_ATOMIC for vmalloc first.  This
ensures caller can sleep.  And for the robustness, even if vmalloc fails,
it should retry with kmalloc to allocate it.

Link: https://lkml.kernel.org/r/173008598713.1262174.2959179484209897252.stgit@mhiramat.roam.corp.google.com
Fixes: aff1871 ("objpool: fix choosing allocation for percpu slots")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Closes: https://lore.kernel.org/all/CAHk-=whO+vSH+XVRio8byJU8idAWES0SPGVZ7KAVdc4qrV0VUA@mail.gmail.com/
Cc: Leo Yan <leo.yan@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Wu <wuqiang.matt@bytedance.com>
Cc: Mikel Rychliski <mikel@mikelr.com>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: mhiramat

lib/objpool.c

@@ -74,15 +74,21 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
 		 * warm caches and TLB hits. in default vmalloc is used to
 		 * reduce the pressure of kernel slab system. as we know,
 		 * mimimal size of vmalloc is one page since vmalloc would
-		 * always align the requested size to page size
+		 * always align the requested size to page size.
+		 * but if vmalloc fails or it is not available (e.g. GFP_ATOMIC)
+		 * allocate percpu slot with kmalloc.
 		 */
-		if ((pool->gfp & GFP_ATOMIC) == GFP_ATOMIC)
-			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
-		else
+		slot = NULL;
+
+		if ((pool->gfp & (GFP_ATOMIC | GFP_KERNEL)) != GFP_ATOMIC)
 			slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
 				cpu_to_node(i), __builtin_return_address(0));
-		if (!slot)
-			return -ENOMEM;
+
+		if (!slot) {
+			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+			if (!slot)
+				return -ENOMEM;
+		}
 		memset(slot, 0, size);
 		pool->cpu_slots[i] = slot;