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[0/1] FOLL_NOWAIT and get_user_pages_unlocked

Message ID 20180302174343.5421-1-aarcange@redhat.com
Headers show
Series FOLL_NOWAIT and get_user_pages_unlocked | expand

Message

Andrea Arcangeli March 2, 2018, 5:43 p.m. UTC 
Hello,

KVM is hanging on postcopy live migration.

David tracked it down to commit
ce53053ce378c21e7ffc45241fd67d6ee79daa2b and the problem is pretty
obvious then.

Either we teach get_user_pages_locked/unlocked to handle FOLL_NOWAIT
(so faultin_nopage works right even when the nonblocking pointer is
not NULL) or we need to revert part of commit
ce53053ce378c21e7ffc45241fd67d6ee79daa2b and keep using FOLL_NOWAIT
only as parameter to get_user_pages (which won't ever set nonblocking
pointer to non-NULL). I suppose the former approach is preferred to be
more robust.

Thanks,
Andrea

Andrea Arcangeli (1):
  mm: gup: teach get_user_pages_unlocked to handle FOLL_NOWAIT

 mm/gup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)