Commit 3f088420 authored Nov 01, 2020 by Shijie Luo Committed by Linus Torvalds Nov 02, 2020

mm: mempolicy: fix potential pte_unmap_unlock pte error



When flags in queue_pages_pte_range don't have MPOL_MF_MOVE or
MPOL_MF_MOVE_ALL bits, code breaks and passing origin pte - 1 to
pte_unmap_unlock seems like not a good idea.

queue_pages_pte_range can run in MPOL_MF_MOVE_ALL mode which doesn't
migrate misplaced pages but returns with EIO when encountering such a
page.  Since commit a7f40cfe ("mm: mempolicy: make mbind() return
-EIO when MPOL_MF_STRICT is specified") and early break on the first pte
in the range results in pte_unmap_unlock on an underflow pte.  This can
lead to lockups later on when somebody tries to lock the pte resp.
page_table_lock again..

Fixes: a7f40cfe ("mm: mempolicy: make mbind() return -EIO when MPOL_MF_STRICT is specified")
Signed-off-by: Shijie Luo <luoshijie1@huawei.com>
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Feilong Lin <linfeilong@huawei.com>
Cc: Shijie Luo <luoshijie1@huawei.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201019074853.50856-1-luoshijie1@huawei.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 58b999d7

mm/mempolicy.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -525,7 +525,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
		unsigned long flags = qp->flags;
		int ret;
		bool has_unmovable = false;
		pte_t *pte;
		pte_t pte, mapped_pte;
		spinlock_t *ptl;

		ptl = pmd_trans_huge_lock(pmd, vma);
		@@ -539,7 +539,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
		if (pmd_trans_unstable(pmd))
		return 0;

		pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
		mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
		for (; addr != end; pte++, addr += PAGE_SIZE) {
		if (!pte_present(*pte))
		continue;
		@@ -571,7 +571,7 @@ static int queue_pages_pte_range(pmd_t *pmd, unsigned long addr,
		} else
		break;
		}
		pte_unmap_unlock(pte - 1, ptl);
		pte_unmap_unlock(mapped_pte, ptl);
		cond_resched();

		if (has_unmovable)

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