mm/migrate: fix race between lock page and clear PG_Isolated

When memory is tight, system may start to compact memory for large
continuous memory demands.  If one process tries to lock a memory page
that is being locked and isolated for compaction, it may wait a long time
or even forever.  This is because compaction will perform non-atomic
PG_Isolated clear while holding page lock, this may overwrite PG_waiters
set by the process that can't obtain the page lock and add itself to the
waiting queue to wait for the lock to be unlocked.

  CPU1                            CPU2
  lock_page(page); (successful)
                                  lock_page(); (failed)
  __ClearPageIsolated(page);      SetPageWaiters(page) (may be overwritten)
  unlock_page(page);

The solution is to not perform non-atomic operation on page flags while
holding page lock.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: andrew.yang <[email protected]>
Cc: Matthias Brugger <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: "Vlastimil Babka" <[email protected]>
Cc: David Howells <[email protected]>
Cc: "William Kucharski" <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Nicholas Tang <[email protected]>
Cc: Kuan-Ying Lee <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions