ucounts: move kfree() out of critical zone protected by ucounts_lock

Although kfree is a non-sleep function, it is possible to enter a long
chain of calls probabilistically, so it looks better to move kfree from
alloc_ucounts() out of the critical zone of ucounts_lock.

Link: https://lkml.kernel.org/r/1733458427-11794-1-git-send-email-mengensun@tencent.com


Signed-off-by: MengEn Sun <mengensun@tencent.com>
Reviewed-by: YueHong Wu <yuehongwu@tencent.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrei Vagin <avagin@google.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>