From: Zi Yan <ziy@xxxxxxxxxx>
Originally, zap_pmd_range() checks pmd value without taking pmd lock.
This can cause pmd_protnone entry not being freed.
Because there are two steps in changing a pmd entry to a pmd_protnone
entry. First, the pmd entry is cleared to a pmd_none entry, then,
the pmd_none entry is changed into a pmd_protnone entry.
The racy check, even with barrier, might only see the pmd_none entry
in zap_pmd_range(), thus, the mapping is neither split nor zapped.
Later, in free_pmd_range(), pmd_none_or_clear() will see the
pmd_protnone entry and clear it as a pmd_bad entry. Furthermore,
since the pmd_protnone entry is not properly freed, the corresponding
deposited pte page table is not freed either.
This causes memory leak or kernel crashing, if VM_BUG_ON() is enabled.
This patch relies on __split_huge_pmd_locked() and
__zap_huge_pmd_locked().
Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
---
mm/memory.c | 24 +++++++++++-------------
1 file changed, 11 insertions(+), 13 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 3929b015faf7..7cfdd5208ef5 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1233,33 +1233,31 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
struct zap_details *details)
{
pmd_t *pmd;
+ spinlock_t *ptl;
unsigned long next;
pmd = pmd_offset(pud, addr);
+ ptl = pmd_lock(vma->vm_mm, pmd);
do {
next = pmd_addr_end(addr, end);
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
VM_BUG_ON_VMA(vma_is_anonymous(vma) &&
!rwsem_is_locked(&tlb->mm->mmap_sem), vma);
- __split_huge_pmd(vma, pmd, addr, false, NULL);
- } else if (zap_huge_pmd(tlb, vma, pmd, addr))
- goto next;
+ __split_huge_pmd_locked(vma, pmd, addr, false);
+ } else if (__zap_huge_pmd_locked(tlb, vma, pmd, addr))
+ continue;
/* fall through */
}
- /*
- * Here there can be other concurrent MADV_DONTNEED or
- * trans huge page faults running, and if the pmd is
- * none or trans huge it can change under us. This is
- * because MADV_DONTNEED holds the mmap_sem in read
- * mode.
- */
- if (pmd_none_or_trans_huge_or_clear_bad(pmd))
- goto next;
+
+ if (pmd_none_or_clear_bad(pmd))
+ continue;
+ spin_unlock(ptl);
next = zap_pte_range(tlb, vma, pmd, addr, next, details);
-next:
cond_resched();
+ spin_lock(ptl);
} while (pmd++, addr = next, addr != end);
+ spin_unlock(ptl);
return addr;
}
--
2.11.0
--
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