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Date: Sat, 17 Oct 2020 09:55:42 +0800 From: Shijie Luo <luoshijie1@...wei.com> To: <osalvador@...e.de>, Michal Hocko <mhocko@...e.com> CC: <akpm@...ux-foundation.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, <linmiaohe@...wei.com>, <linfeilong@...wei.com> Subject: Re: [PATCH] mm: fix potential pte_unmap_unlock pte error On 2020/10/16 22:05, osalvador@...e.de wrote: > On 2020-10-16 15:42, Michal Hocko wrote: >> OK, I finally managed to convince my friday brain to think and grasped >> what the code is intended to do. The loop is hairy and we want to >> prevent from spurious EIO when all the pages are on a proper node. So >> the check has to be done inside the loop. Anyway I would find the >> following fix less error prone and easier to follow >> diff --git a/mm/mempolicy.c b/mm/mempolicy.c >> index eddbe4e56c73..8cc1fc9c4d13 100644 >> --- a/mm/mempolicy.c >> +++ b/mm/mempolicy.c >> @@ -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) > > It is more clear to grasp, definitely. Yeah, this one is more comprehensible, I 'll send a v2 patch, thank you.
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