mm/memcg: disable migration instead of preemption in drain_all_stock().

Before the for-each-CPU loop, preemption is disabled so that so that
drain_local_stock() can be invoked directly instead of scheduling a
worker.  Ensuring that drain_local_stock() completed on the local CPU is
not correctness problem.  It _could_ be that the charging path will be
forced to reclaim memory because cached charges are still waiting for
their draining.

Disabling preemption before invoking drain_local_stock() is problematic
on PREEMPT_RT due to the sleeping locks involved.  To ensure that no CPU
migrations happens across for_each_online_cpu() it is enouhg to use
migrate_disable() which disables migration and keeps context preemptible
to a sleeping lock can be acquired.  A race with CPU hotplug is not a
problem because pcp data is not going away.  In the worst case we just
schedule draining of an empty stock.

Use migrate_disable() instead of get_cpu() around the
for_each_online_cpu() loop.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: kernel test robot <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Michal Koutný <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Waiman Long <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions