On Wed, May 16, 2018 at 06:59:35PM +0800, Amy Chiang wrote:
> In add_stripe_bio(), if the stripe_head is in batch list, the incoming
> bio is regarded as overlapping, and the bit R5_Overlap on this stripe_head
> is set. break_stripe_batch_list() checks bit R5_Overlap on each stripe_head
> first then assigns NULL to sh->batch_head.
>
> If break_stripe_batch_list() checks bit R5_Overlap on stripe_head A
> after add_stripe_bio() finds stripe_head A is in batch list and before
> add_stripe_bio() sets bit R5_Overlapt of stripe_head A,
> break_stripe_batch_list() would not know there's a process in
> wait_for_overlap and needs to call wake_up(). There's a huge chance a
> process never returns from schedule() if add_stripe_bio() is called
> from raid5_make_request().
>
> In break_stripe_batch_list(), assigning NULL to sh->batch_head should
> be done before it checks bit R5_Overlap of a stripe_head.
Applied, thanks!
> Signed-off-by: Amy Chiang <amychiang@xxxxxxxx>
> ---
> drivers/md/raid5.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 928e24a..65f9af0 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -4611,15 +4611,15 @@ static void break_stripe_batch_list(struct stripe_head *head_sh,
>
> sh->check_state = head_sh->check_state;
> sh->reconstruct_state = head_sh->reconstruct_state;
> + spin_lock_irq(&sh->stripe_lock);
> + sh->batch_head = NULL;
> + spin_unlock_irq(&sh->stripe_lock);
> for (i = 0; i < sh->disks; i++) {
> if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
> do_wakeup = 1;
> sh->dev[i].flags = head_sh->dev[i].flags &
> (~((1 << R5_WriteError) | (1 << R5_Overlap)));
> }
> - spin_lock_irq(&sh->stripe_lock);
> - sh->batch_head = NULL;
> - spin_unlock_irq(&sh->stripe_lock);
> if (handle_flags == 0 ||
> sh->state & handle_flags)
> set_bit(STRIPE_HANDLE, &sh->state);
> --
> 2.7.4
>
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