From: Oleg Nesterov <oleg@xxxxxxxxxx> Subject: swap_readpage(): avoid blk_wake_io_task() if !synchronous 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(). Link: http://lkml.kernel.org/r/20190704160301.GA5956@xxxxxxxxxx Fixes: 0619317ff8baa2d ("block: add polled wakeup task helper") Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx> Reported-by: Qian Cai <cai@xxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Reviewed-by: Jens Axboe <axboe@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_io.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) --- a/mm/page_io.c~swap_readpage-avoid-blk_wake_io_task-if-synchronous +++ a/mm/page_io.c @@ -137,8 +137,10 @@ out: 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, @@ -395,11 +397,12 @@ int swap_readpage(struct page *page, boo * 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); _
