On Wed, 5 Jun 2019, Jens Axboe wrote:
>
> How about the following plan - if folks are happy with this sched patch,
> we can queue it up for 5.3. Once that is in, I'll kill the block change
> that special cases the polled task wakeup. For 5.2, we go with Oleg's
> patch for the swap case.
I just hit the do_task_dead() kernel BUG at kernel/sched/core.c:3463!
while heavy swapping on 5.2-rc7: it looks like Oleg's patch intended
for 5.2 was not signed off, and got forgotten.
I did hit the do_task_dead() BUG (but not at all easily) on early -rcs
before seeing Oleg's patch, then folded it in and and didn't hit the BUG
again; then just tried again without it, and luckily hit in a few hours.
So I can give it an enthusiastic
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
because it makes good sense to avoid the get/blk_wake/put overhead on
the asynch path anyway, even if it didn't work around a bug; but only
Half-Tested-by: Hugh Dickins <hughd@xxxxxxxxxx>
since I have not been exercising the synchronous path at all.
Hugh, requoting Oleg:
>
> I don't understand this code at all but I am just curious, can we do
> something like incomplete patch below ?
>
> Oleg.
>
> --- x/mm/page_io.c
> +++ x/mm/page_io.c
> @@ -140,8 +140,10 @@ int swap_readpage(struct page *page, bool synchronous)
> 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, 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);
