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/[e-mail]
Fixes: aff1871bfc81 ("objpool: fix choosing allocation for percpu slots")
Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
Reported-by: Linus Torvalds <[e-mail]>
Closes: https://lore.kernel.org/all/CAHk-=[e-mail]/
Cc: Leo Yan <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Matt Wu <[e-mail]>
Cc: Mikel Rychliski <[e-mail]>
Cc: Steven Rostedt (Google) <[e-mail]>
Cc: Viktor Malik <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

lib/objpool.c

···
 		 * 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;