swap_readpage() sets waiter = bio->bi_private even if synchronous = F, this means that the caller can get the spurious wakeup after return. This can be fatal if blk_wake_io_task() does set_current_state(TASK_RUNNING) after the caller does set_special_state(), in the worst case the kernel can crash in do_task_dead().
Reported-by: Qian Cai <[email protected]> Acked-by: Hugh Dickins <[email protected]> Reviewed-by: Jens Axboe <[email protected]> Signed-off-by: Oleg Nesterov <[email protected]> --- mm/page_io.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/page_io.c b/mm/page_io.c index 2e8019d..3098895 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -140,8 +140,10 @@ static void end_swap_bio_read(struct bio *bio) unlock_page(page); WRITE_ONCE(bio->bi_private, NULL); bio_put(bio); - blk_wake_io_task(waiter); - put_task_struct(waiter); + if (waiter) { + blk_wake_io_task(waiter); + put_task_struct(waiter); + } } int generic_swapfile_activate(struct swap_info_struct *sis, @@ -398,11 +400,12 @@ int swap_readpage(struct page *page, bool synchronous) * Keep this task valid during swap readpage because the oom killer may * attempt to access it in the page fault retry time check. */ - get_task_struct(current); - bio->bi_private = current; bio_set_op_attrs(bio, REQ_OP_READ, 0); - if (synchronous) + if (synchronous) { bio->bi_opf |= REQ_HIPRI; + get_task_struct(current); + bio->bi_private = current; + } count_vm_event(PSWPIN); bio_get(bio); qc = submit_bio(bio); -- 2.5.0
