From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Subject: mm: drop NULL return check of pte_offset_map_lock()
pte_offset_map_lock() finds and takes ptl, and returns pte. But some
callers return without unlocking the ptl when pte == NULL, which seems
weird.
Git history said that !pte check in change_pte_range() was introduced in
commit 1ad9f620c3a2 ("mm: numa: recheck for transhuge pages under lock
during protection changes") and still remains after commit 175ad4f1e7a2
("mm: mprotect: use pmd_trans_unstable instead of taking the pmd_lock")
which partially reverts 1ad9f620c3a2. So I think that it's just dead
code.
Many other caller of pte_offset_map_lock() never check NULL return, so
let's do likewise.
Link: http://lkml.kernel.org/r/1495089737-1292-1-git-send-email-n-horiguchi@xxxxxxxxxxxxx
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memory.c | 2 --
mm/mprotect.c | 2 --
2 files changed, 4 deletions(-)
diff -puN mm/memory.c~mm-drop-null-return-check-of-pte_offset_map_lock mm/memory.c
--- a/mm/memory.c~mm-drop-null-return-check-of-pte_offset_map_lock
+++ a/mm/memory.c
@@ -4014,8 +4014,6 @@ static int __follow_pte_pmd(struct mm_st
goto out;
ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
- if (!ptep)
- goto out;
if (!pte_present(*ptep))
goto unlock;
*ptepp = ptep;
diff -puN mm/mprotect.c~mm-drop-null-return-check-of-pte_offset_map_lock mm/mprotect.c
--- a/mm/mprotect.c~mm-drop-null-return-check-of-pte_offset_map_lock
+++ a/mm/mprotect.c
@@ -58,8 +58,6 @@ static unsigned long change_pte_range(st
* reading.
*/
pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
- if (!pte)
- return 0;
/* Get target node for single threaded private VMAs */
if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
_
--
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