mm/memcg: Protect memcg_stock with a local_lock_t

mm/memcg: Protect memcg_stock with a local_lock_t

The members of the per-CPU structure memcg_stock_pcp are protected by
disabling interrupts. This is not working on PREEMPT_RT because it
creates atomic context in which actions are performed which require
preemptible context. One example is obj_cgroup_release().

The IRQ-disable sections can be replaced with local_lock_t which
preserves the explicit disabling of interrupts while keeps the code
preemptible on PREEMPT_RT.

drain_obj_stock() drops a reference on obj_cgroup which leads to an invocat=
ion
of obj_cgroup_release() if it is the last object. This in turn leads to
recursive locking of the local_lock_t. To avoid this, obj_cgroup_release() =
is
invoked outside of the locked section.

obj_cgroup_uncharge_pages() can be invoked with the local_lock_t acquired a=
nd
without it. This will lead later to a recursion in refill_stock(). To
avoid the locking recursion provide obj_cgroup_uncharge_pages_locked()
which uses the locked version of refill_stock().

- Replace disabling interrupts for memcg_stock with a local_lock_t.

- Let drain_obj_stock() return the old struct obj_cgroup which is passed
  to obj_cgroup_put() outside of the locked section.

- Provide obj_cgroup_uncharge_pages_locked() which uses the locked
  version of refill_stock() to avoid recursive locking in
  drain_obj_stock().

Link: https://lkml.kernel.org/r/20220209014709.GA26885@xsang-OptiPlex-9020
Link: https://lkml.kernel.org/r/20220226204144.1008339-6-bigeasy@linutronix.de
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>