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UPSTREAM: mm: prevent userfaults to be handled under per-vma lock

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Due to the possibility of handle_userfault dropping mmap_lock, avoid fault
handling under VMA lock and retry holding mmap_lock.  This can be handled
more gracefully in the future.

Link: https://lkml.kernel.org/r/20230227173632.3292573-28-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

(cherry picked from commit 444eeb17437a0ef526c606e9141a415d3b7dfddd)

Bug: 161210518
Change-Id: I383603d637497ea9917ad08908530f91052a17cc
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
This commit is contained in:
Suren Baghdasaryan 2023-02-27 09:36:26 -08:00 committed by Carlos Llamas
parent 6e306e82ac
commit 4e4c6989ae
1 changed files with 9 additions and 0 deletions
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9
mm/memory.c
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@ -5296,6 +5296,15 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
if (!vma_start_read(vma))
goto inval;
/*
* Due to the possibility of userfault handler dropping mmap_lock, avoid
* it for now and fall back to page fault handling under mmap_lock.
*/
if (userfaultfd_armed(vma)) {
vma_end_read(vma);
goto inval;
}
/* Check since vm_start/vm_end might change before we lock the VMA */
if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
vma_end_read(vma);