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authorJann Horn <[email protected]>2024-08-13 22:25:22 +0200
committerAndrew Morton <[email protected]>2024-09-01 17:59:00 -0700
commit4828d207dc5161dc7ddf9a4f6dcfd80c7dd7d20a (patch)
tree8dc1897967f79d74885f6abd07af6de02c538d60
parent71c186efc1b2cf1aeabfeff3b9bd5ac4c5ac14d8 (diff)
userfaultfd: don't BUG_ON() if khugepaged yanks our page table
Since khugepaged was changed to allow retracting page tables in file mappings without holding the mmap lock, these BUG_ON()s are wrong - get rid of them. We could also remove the preceding "if (unlikely(...))" block, but then we could reach pte_offset_map_lock() with transhuge pages not just for file mappings but also for anonymous mappings - which would probably be fine but I think is not necessarily expected. Link: https://lkml.kernel.org/r/[email protected] Fixes: 1d65b771bc08 ("mm/khugepaged: retract_page_tables() without mmap or vma lock") Signed-off-by: Jann Horn <[email protected]> Reviewed-by: Qi Zheng <[email protected]> Acked-by: David Hildenbrand <[email protected]> Cc: Andrea Arcangeli <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Pavel Emelyanov <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
-rw-r--r--mm/userfaultfd.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 290b2a0d84ac..acc56c75ba99 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -807,9 +807,10 @@ retry:
err = -EFAULT;
break;
}
-
- BUG_ON(pmd_none(*dst_pmd));
- BUG_ON(pmd_trans_huge(*dst_pmd));
+ /*
+ * For shmem mappings, khugepaged is allowed to remove page
+ * tables under us; pte_offset_map_lock() will deal with that.
+ */
err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr,
src_addr, flags, &folio);