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Subject[PATCH v2 2/3] mm/swapfile: fix possible data races of inuse_pages
Date
si->inuse_pages could still be accessed concurrently now. The plain reads
outside si->lock critical section, i.e. swap_show and si_swapinfo, which
results in data races. But these should be ok because they're just used
for showing swap info.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
---
mm/swapfile.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d2bead7b8b70..3fa26f6971e9 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2646,7 +2646,7 @@ static int swap_show(struct seq_file *swap, void *v)
}

bytes = si->pages << (PAGE_SHIFT - 10);
- inuse = si->inuse_pages << (PAGE_SHIFT - 10);
+ inuse = READ_ONCE(si->inuse_pages) << (PAGE_SHIFT - 10);

file = si->swap_file;
len = seq_file_path(swap, file, " \t\n\\");
@@ -3265,7 +3265,7 @@ void si_swapinfo(struct sysinfo *val)
struct swap_info_struct *si = swap_info[type];

if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
- nr_to_be_unused += si->inuse_pages;
+ nr_to_be_unused += READ_ONCE(si->inuse_pages);
}
val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
val->totalswap = total_swap_pages + nr_to_be_unused;
--
2.23.0
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