linux-kernel - [PATCH v3 3/4] mm/swap: remove confusing checking for non_swap_entry() in swap_ra

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Date:   Tue, 20 Apr 2021 09:30:47 -0400
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>
CC:     <ying.huang@...el.com>, <dennis@...nel.org>,
        <tim.c.chen@...ux.intel.com>, <hughd@...gle.com>,
        <hannes@...xchg.org>, <mhocko@...e.com>, <iamjoonsoo.kim@....com>,
        <alexs@...nel.org>, <willy@...radead.org>, <minchan@...nel.org>,
        <richard.weiyang@...il.com>, <shy828301@...il.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH v3 3/4] mm/swap: remove confusing checking for non_swap_entry() in swap_ra_info()

The non_swap_entry() was used for working with VMA based swap readahead
via commit ec560175c0b6 ("mm, swap: VMA based swap readahead"). Then it's
moved to swap_ra_info() since commit eaf649ebc3ac ("mm: swap: clean up swap
readahead"). But this makes the code confusing. The non_swap_entry() check
looks racy because while we released the pte lock, somebody else might have
faulted in this pte. So we should check whether it's swap pte first to
guard against such race or swap_type will be unexpected. But the swap_entry
isn't used in this function and we will have enough checking when we really
operate the PTE entries later. So checking for non_swap_entry() is not
really needed here and should be removed to avoid confusion.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/swap_state.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 272ea2108c9d..df5405384520 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -721,7 +721,6 @@ static void swap_ra_info(struct vm_fault *vmf,
 {
 	struct vm_area_struct *vma = vmf->vma;
 	unsigned long ra_val;
-	swp_entry_t entry;
 	unsigned long faddr, pfn, fpfn;
 	unsigned long start, end;
 	pte_t *pte, *orig_pte;
@@ -739,11 +738,6 @@ static void swap_ra_info(struct vm_fault *vmf,

 	faddr = vmf->address;
 	orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
-	entry = pte_to_swp_entry(*pte);
-	if ((unlikely(non_swap_entry(entry)))) {
-		pte_unmap(orig_pte);
-		return;
-	}

 	fpfn = PFN_DOWN(faddr);
 	ra_val = GET_SWAP_RA_VAL(vma);
-- 
2.19.1