David Hildenbrand <david@xxxxxxxxxx> writes: > On 22.05.23 09:09, Huang Ying wrote: >> The general rule to use a swap entry is as follows. >> When we get a swap entry, if there isn't some other way to prevent >> swapoff, such as page lock for swap cache, page table lock, etc., the >> swap entry may become invalid because of swapoff. Then, we need to >> enclose all swap related functions with get_swap_device() and >> put_swap_device(), unless the swap functions call >> get/put_swap_device() by themselves. >> Add the rule as comments of get_swap_device(). >> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> >> Cc: David Hildenbrand <david@xxxxxxxxxx> >> Cc: Hugh Dickins <hughd@xxxxxxxxxx> >> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> >> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> >> Cc: Michal Hocko <mhocko@xxxxxxxx> >> Cc: Minchan Kim <minchan@xxxxxxxxxx> >> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> >> Cc: Yang Shi <shy828301@xxxxxxxxx> >> Cc: Yu Zhao <yuzhao@xxxxxxxxxx> >> --- >> mm/swapfile.c | 12 +++++++++--- >> 1 file changed, 9 insertions(+), 3 deletions(-) >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> index 4dbaea64635d..0c1cb935b2eb 100644 >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -1219,6 +1219,13 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, >> } >> /* >> + * When we get a swap entry, if there isn't some other way to prevent >> + * swapoff, such as page lock for swap cache, page table lock, etc., > > Again "page lock for swap cache" might be imprecise. Sure. Will revise this. >> + * the swap entry may become invalid because of swapoff. Then, we >> + * need to enclose all swap related functions with get_swap_device() >> + * and put_swap_device(), unless the swap functions call >> + * get/put_swap_device() by themselves. >> + * >> * Check whether swap entry is valid in the swap device. If so, >> * return pointer to swap_info_struct, and keep the swap entry valid >> * via preventing the swap device from being swapoff, until >> @@ -1227,9 +1234,8 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p, >> * Notice that swapoff or swapoff+swapon can still happen before the >> * percpu_ref_tryget_live() in get_swap_device() or after the >> * percpu_ref_put() in put_swap_device() if there isn't any other way >> - * to prevent swapoff, such as page lock, page table lock, etc. The >> - * caller must be prepared for that. For example, the following >> - * situation is possible. >> + * to prevent swapoff. The caller must be prepared for that. For >> + * example, the following situation is possible. >> * >> * CPU1 CPU2 >> * do_swap_page() > > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Thanks! Best Regards, Huang, Ying
