* + swap-fix-do_swap_page-race-with-swapoff.patch added to -mm tree
@ 2021-05-10 0:49 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2021-05-10 0:49 UTC (permalink / raw)
To: alexs, david, dennis, hannes, hughd, iamjoonsoo.kim, linmiaohe,
mhocko, minchan, mm-commits, richard.weiyang, shy828301,
tim.c.chen, willy, ying.huang, yuzhao
The patch titled
Subject: swap: fix do_swap_page() race with swapoff
has been added to the -mm tree. Its filename is
swap-fix-do_swap_page-race-with-swapoff.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/swap-fix-do_swap_page-race-with-swapoff.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/swap-fix-do_swap_page-race-with-swapoff.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: swap: fix do_swap_page() race with swapoff
When I was investigating the swap code, I found the below possible race
window:
CPU 1 CPU 2
----- -----
do_swap_page
if (data_race(si->flags & SWP_SYNCHRONOUS_IO)
swap_readpage
if (data_race(sis->flags & SWP_FS_OPS)) {
swapoff
..
p->swap_file = NULL;
..
struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;[oops!]
Note that for the pages that are swapped in through swap cache, this isn't
an issue. Because the page is locked, and the swap entry will be marked
with SWAP_HAS_CACHE, so swapoff() can not proceed until the page has been
unlocked.
Fix this race by using get/put_swap_device() to guard against concurrent
swapoff.
Link: https://lkml.kernel.org/r/20210426123316.806267-3-linmiaohe@huawei.com
Fixes: 0bcac06f27d7 ("mm,swap: skip swapcache for swapin of synchronous device")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/swap.h | 9 +++++++++
mm/memory.c | 11 +++++++++--
2 files changed, 18 insertions(+), 2 deletions(-)
--- a/include/linux/swap.h~swap-fix-do_swap_page-race-with-swapoff
+++ a/include/linux/swap.h
@@ -527,6 +527,15 @@ static inline struct swap_info_struct *s
return NULL;
}
+static inline struct swap_info_struct *get_swap_device(swp_entry_t entry)
+{
+ return NULL;
+}
+
+static inline void put_swap_device(struct swap_info_struct *si)
+{
+}
+
#define swap_address_space(entry) (NULL)
#define get_nr_swap_pages() 0L
#define total_swap_pages 0L
--- a/mm/memory.c~swap-fix-do_swap_page-race-with-swapoff
+++ a/mm/memory.c
@@ -3311,6 +3311,7 @@ vm_fault_t do_swap_page(struct vm_fault
{
struct vm_area_struct *vma = vmf->vma;
struct page *page = NULL, *swapcache;
+ struct swap_info_struct *si = NULL;
swp_entry_t entry;
pte_t pte;
int locked;
@@ -3338,14 +3339,16 @@ vm_fault_t do_swap_page(struct vm_fault
goto out;
}
+ /* Prevent swapoff from happening to us. */
+ si = get_swap_device(entry);
+ if (unlikely(!si))
+ goto out;
delayacct_set_flag(current, DELAYACCT_PF_SWAPIN);
page = lookup_swap_cache(entry, vma, vmf->address);
swapcache = page;
if (!page) {
- struct swap_info_struct *si = swp_swap_info(entry);
-
if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
__swap_count(entry) == 1) {
/* skip swapcache */
@@ -3514,6 +3517,8 @@ vm_fault_t do_swap_page(struct vm_fault
unlock:
pte_unmap_unlock(vmf->pte, vmf->ptl);
out:
+ if (si)
+ put_swap_device(si);
return ret;
out_nomap:
pte_unmap_unlock(vmf->pte, vmf->ptl);
@@ -3525,6 +3530,8 @@ out_release:
unlock_page(swapcache);
put_page(swapcache);
}
+ if (si)
+ put_swap_device(si);
return ret;
}
_
Patches currently in -mm which might be from linmiaohe@huawei.com are
mm-swapfile-use-percpu_ref-to-serialize-against-concurrent-swapoff.patch
swap-fix-do_swap_page-race-with-swapoff.patch
mm-swap-remove-confusing-checking-for-non_swap_entry-in-swap_ra_info.patch
mm-shmem-fix-shmem_swapin-race-with-swapoff.patch
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2021-05-10 0:49 + swap-fix-do_swap_page-race-with-swapoff.patch added to -mm tree akpm
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