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authorAndrea Arcangeli <aarcange@redhat.com>2018-03-09 15:51:06 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-03-09 16:40:01 -0800
commit96312e61282ae3f6537a562625706498cbc75594 (patch)
treecee11a490bf11d43696eaa577837839abd116cd6
parent1b4cfe3c0a30dde968fb43c577a8d7e262a145ee (diff)
mm/gup.c: teach get_user_pages_unlocked to handle FOLL_NOWAIT
KVM is hanging during postcopy live migration with userfaultfd because get_user_pages_unlocked is not capable to handle FOLL_NOWAIT. Earlier FOLL_NOWAIT was only ever passed to get_user_pages. Specifically faultin_page (the callee of get_user_pages_unlocked caller) doesn't know that if FAULT_FLAG_RETRY_NOWAIT was set in the page fault flags, when VM_FAULT_RETRY is returned, the mmap_sem wasn't actually released (even if nonblocking is not NULL). So it sets *nonblocking to zero and the caller won't release the mmap_sem thinking it was already released, but it wasn't because of FOLL_NOWAIT. Link: http://lkml.kernel.org/r/20180302174343.5421-2-aarcange@redhat.com Fixes: ce53053ce378c ("kvm: switch get_user_page_nowait() to get_user_pages_unlocked()") Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Tested-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/gup.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/mm/gup.c b/mm/gup.c
index 1b46e6e74881..6afae32571ca 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -516,7 +516,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
}
if (ret & VM_FAULT_RETRY) {
- if (nonblocking)
+ if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
*nonblocking = 0;
return -EBUSY;
}
@@ -890,7 +890,10 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
break;
}
if (*locked) {
- /* VM_FAULT_RETRY didn't trigger */
+ /*
+ * VM_FAULT_RETRY didn't trigger or it was a
+ * FOLL_NOWAIT.
+ */
if (!pages_done)
pages_done = ret;
break;