diff options
authorVinayak Menon <vinmenon@codeaurora.org>2019-11-15 17:35:00 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-12-01 09:17:35 +0100
commit006360ec33d9387610f641c633aef0e523753b8d (patch)
parent16a300fb1dbb119023275798bbd749c3a3a54d18 (diff)
mm/page_io.c: do not free shared swap slots
[ Upstream commit 5df373e95689b9519b8557da7c5bd0db0856d776 ] The following race is observed due to which a processes faulting on a swap entry, finds the page neither in swapcache nor swap. This causes zram to give a zero filled page that gets mapped to the process, resulting in a user space crash later. Consider parent and child processes Pa and Pb sharing the same swap slot with swap_count 2. Swap is on zram with SWP_SYNCHRONOUS_IO set. Virtual address 'VA' of Pa and Pb points to the shared swap entry. Pa Pb fault on VA fault on VA do_swap_page do_swap_page lookup_swap_cache fails lookup_swap_cache fails Pb scheduled out swapin_readahead (deletes zram entry) swap_free (makes swap_count 1) Pb scheduled in swap_readpage (swap_count == 1) Takes SWP_SYNCHRONOUS_IO path zram enrty absent zram gives a zero filled page Fix this by making sure that swap slot is freed only when swap count drops down to one. Link: http://lkml.kernel.org/r/1571743294-14285-1-git-send-email-vinmenon@codeaurora.org Fixes: aa8d22a11da9 ("mm: swap: SWP_SYNCHRONOUS_IO: skip swapcache only if swapped page has no other reference") Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org> Suggested-by: Minchan Kim <minchan@google.com> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Hugh Dickins <hughd@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
1 files changed, 4 insertions, 3 deletions
diff --git a/mm/page_io.c b/mm/page_io.c
index aafd19ec1db4..08d2eae58fce 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -76,6 +76,7 @@ static void swap_slot_free_notify(struct page *page)
struct swap_info_struct *sis;
struct gendisk *disk;
+ swp_entry_t entry;
* There is no guarantee that the page is in swap cache - the software
@@ -107,11 +108,11 @@ static void swap_slot_free_notify(struct page *page)
* we again wish to reclaim it.
disk = sis->bdev->bd_disk;
- if (disk->fops->swap_slot_free_notify) {
- swp_entry_t entry;
+ entry.val = page_private(page);
+ if (disk->fops->swap_slot_free_notify &&
+ __swap_count(sis, entry) == 1) {
unsigned long offset;
- entry.val = page_private(page);
offset = swp_offset(entry);