On 24.07.19 00:58, Halil Pasic wrote:
> The access to airq_areas was racy ever since the adapter interrupts got
> introduced to virtio-ccw, but since commit 39c7dcb15892 ("virtio/s390:
> make airq summary indicators DMA") this became an issue in practice as
> well. Namely before that commit the airq_info that got overwritten was
> still functional. After that commit however the two infos share a
> summary_indicator, which aggravates the situation. Which means
> auto-online mechanism occasionally hangs the boot with virtio_blk.
>
> Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
> Reported-by: Marc Hartmayer <mhartmay@xxxxxxxxxxxxx>
> Fixes: 96b14536d935 ("virtio-ccw: virtio-ccw adapter interrupt support.")
> ---
> * We need definitely this fixed for 5.3. For older stable kernels it is
> to be discussed. @Connie what do you think: do we need a cc stable?
Unless you can prove that the problem could never happen on old version
we absolutely do need cc stable.
>
> * I have a variant that does not need the extra mutex but uses cmpxchg().
> Decided to post this one because that one is more complex. But if there
> is interest we can have a look at it as well.
This is slow path (startup) and never called in hot path. Correct? Mutex should be
fine.
> ---
> drivers/s390/virtio/virtio_ccw.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> index 1a55e5942d36..d97742662755 100644
> --- a/drivers/s390/virtio/virtio_ccw.c
> +++ b/drivers/s390/virtio/virtio_ccw.c
> @@ -145,6 +145,8 @@ struct airq_info {
> struct airq_iv *aiv;
> };
> static struct airq_info *airq_areas[MAX_AIRQ_AREAS];
> +DEFINE_MUTEX(airq_areas_lock);
> +
> static u8 *summary_indicators;
>
> static inline u8 *get_summary_indicator(struct airq_info *info)
> @@ -265,9 +267,11 @@ static unsigned long get_airq_indicator(struct virtqueue *vqs[], int nvqs,
> unsigned long bit, flags;
>
> for (i = 0; i < MAX_AIRQ_AREAS && !indicator_addr; i++) {
> + mutex_lock(&airq_areas_lock);
> if (!airq_areas[i])
> airq_areas[i] = new_airq_info(i);
> info = airq_areas[i];
> + mutex_unlock(&airq_areas_lock);
> if (!info)
> return 0;
> write_lock_irqsave(&info->lock, flags);
>
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