From: Huang Ying ying.huang@intel.com
[ Upstream commit aeb309b81c6bada783c3695528a3e10748e97285 ]
Via commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks"), after swapoff, the address_space associated with the swap device will be freed. So swap_address_space() users which touch the address_space need some kind of mechanism to prevent the address_space from being freed during accessing.
When mincore processes an unmapped range for swapped shmem pages, it doesn't hold the lock to prevent swap device from being swapped off. So the following race is possible:
CPU1 CPU2 do_mincore() swapoff() walk_page_range() mincore_unmapped_range() __mincore_unmapped_range mincore_page as = swap_address_space() ... exit_swap_address_space() ... kvfree(spaces) find_get_page(as)
The address space may be accessed after being freed.
To fix the race, get_swap_device()/put_swap_device() is used to enclose find_get_page() to check whether the swap entry is valid and prevent the swap device from being swapoff during accessing.
Link: http://lkml.kernel.org/r/20190611020510.28251-1-ying.huang@intel.com Fixes: 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks") Signed-off-by: "Huang, Ying" ying.huang@intel.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Acked-by: Michal Hocko mhocko@suse.com Cc: Hugh Dickins hughd@google.com Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Minchan Kim minchan@kernel.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Mel Gorman mgorman@techsingularity.net Cc: Jérôme Glisse jglisse@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Yang Shi yang.shi@linux.alibaba.com Cc: David Rientjes rientjes@google.com Cc: Rik van Riel riel@redhat.com Cc: Jan Kara jack@suse.cz Cc: Dave Jiang dave.jiang@intel.com Cc: Daniel Jordan daniel.m.jordan@oracle.com Cc: Andrea Parri andrea.parri@amarulasolutions.com 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 --- mm/mincore.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/mm/mincore.c b/mm/mincore.c index c3f058bd0faf..4fe91d497436 100644 --- a/mm/mincore.c +++ b/mm/mincore.c @@ -68,8 +68,16 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff) */ if (xa_is_value(page)) { swp_entry_t swp = radix_to_swp_entry(page); - page = find_get_page(swap_address_space(swp), - swp_offset(swp)); + struct swap_info_struct *si; + + /* Prevent swap device to being swapoff under us */ + si = get_swap_device(swp); + if (si) { + page = find_get_page(swap_address_space(swp), + swp_offset(swp)); + put_swap_device(si); + } else + page = NULL; } } else page = find_get_page(mapping, pgoff);