debugobjects: Don't wake up kswapd from fill_pool()

syzbot is reporting a lockdep warning in fill_pool() because the allocation
from debugobjects is using GFP_ATOMIC, which is (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)
and therefore tries to wake up kswapd, which acquires kswapd_wait::lock.

Since fill_pool() might be called with arbitrary locks held, fill_pool()
should not assume that acquiring kswapd_wait::lock is safe.

Use __GFP_HIGH instead and remove __GFP_NORETRY as it is pointless for
!__GFP_DIRECT_RECLAIM allocation.

Fixes: 3ac7fe5 ("infrastructure to debug (dynamic) objects")
Reported-by: syzbot <syzbot+fe0c72f0ccbb93786380@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/6577e1fa-b6ee-f2be-2414-a2b51b1c5e30@I-love.SAKURA.ne.jp
Closes: https://syzkaller.appspot.com/bug?extid=fe0c72f0ccbb93786380

Author: Tetsuo Handa

lib/debugobjects.c

@@ -126,7 +126,7 @@ static const char *obj_states[ODEBUG_STATE_MAX] = {
 
 static void fill_pool(void)
 {
-	gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
+	gfp_t gfp = __GFP_HIGH | __GFP_NOWARN;
 	struct debug_obj *obj;
 	unsigned long flags;