[PATCH] objpool: fix choosing allocation for percpu slots

[Viktor Malik <vmalik@redhat.com>]

objpool intends to use vmalloc for default (non-atomic) allocations of
percpu slots and objects. However, the condition checking if GFP flags
are equal to GFP_ATOMIC is wrong and causes kmalloc to be used in most
cases (even if GFP_KERNEL is requested). Since kmalloc cannot allocate
large amounts of memory, this may lead to unexpected OOM errors.

For instance, objpool is used by fprobe rethook which in turn is used by
BPF kretprobe.multi and kprobe.session probe types. Trying to attach
these to all kernel functions with libbpf using

    SEC("kprobe.session/*")
    int kprobe(struct pt_regs *ctx)
    {
        [...]
    }

fails on objpool slot allocation with ENOMEM.

Fix the condition to truly use vmalloc by default.

Fixes: b4edb8d2d464 ("lib: objpool added: ring-array based lockless MPMC")
Signed-off-by: Viktor Malik <vmalik@redhat.com>
---
 lib/objpool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/objpool.c b/lib/objpool.c
index 234f9d0bd081..fd108fe0d095 100644
--- a/lib/objpool.c
+++ b/lib/objpool.c
@@ -76,7 +76,7 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
 		 * mimimal size of vmalloc is one page since vmalloc would
 		 * always align the requested size to page size
 		 */
-		if (pool->gfp & GFP_ATOMIC)
+		if ((pool->gfp & GFP_ATOMIC) == GFP_ATOMIC)
 			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
 		else
 			slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
-- 
2.46.0