Re: [Xen-devel] [PATCH 1/3] xen/blkback: fix disconnect while I/Os in flight

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx>]

Am Dienstag, 16. Mai 2017, 08:23:18 schrieb Juergen Gross:
> Today disconnecting xen-blkback is broken in case there are still
> I/Os in flight: xen_blkif_disconnect() will bail out early without
> releasing all resources in the hope it will be called again when
> the last request has terminated. This, however, won't happen as
> xen_blkif_free() won't be called on termination of the last running
> request: xen_blkif_put() won't decrement the blkif refcnt to 0 as
> xen_blkif_disconnect() didn't finish before thus some xen_blkif_put()
> calls in xen_blkif_disconnect() didn't happen.
> 
> To solve this deadlock xen_blkif_disconnect() and
> xen_blkif_alloc_rings() shouldn't use xen_blkif_put() and
> xen_blkif_get() but use some other way to do their accounting of
> resources.
> 
> This at once fixes another error in xen_blkif_disconnect(): when it
> returned early with -EBUSY for another ring than 0 it would call
> xen_blkif_put() again for already handled rings on a subsequent call.
> This will lead to inconsistencies in the refcnt handling.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Glenn Enright <glenn@xxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Tested-by: Steven Haigh <netwiz@xxxxxxxxx>
> ---
>  drivers/block/xen-blkback/common.h | 1 +
>  drivers/block/xen-blkback/xenbus.c | 7 +++++--
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/common.h 
> b/drivers/block/xen-blkback/common.h
> index dea61f6ab8cb..953f38802333 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -281,6 +281,7 @@ struct xen_blkif_ring {
>  
>       wait_queue_head_t       wq;
>       atomic_t                inflight;
> +     int                     active;

Maybe better using bool?

Dietmar.

>       /* One thread per blkif ring. */
>       struct task_struct      *xenblkd;
>       unsigned int            waiting_reqs;
> diff --git a/drivers/block/xen-blkback/xenbus.c 
> b/drivers/block/xen-blkback/xenbus.c
> index 1f3dfaa54d87..e68df9de8858 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -159,7 +159,7 @@ static int xen_blkif_alloc_rings(struct xen_blkif *blkif)
>               init_waitqueue_head(&ring->shutdown_wq);
>               ring->blkif = blkif;
>               ring->st_print = jiffies;
> -             xen_blkif_get(blkif);
> +             ring->active = 1;
>       }
>  
>       return 0;
> @@ -249,6 +249,9 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>               struct xen_blkif_ring *ring = &blkif->rings[r];
>               unsigned int i = 0;
>  
> +             if (!ring->active)
> +                     continue;
> +
>               if (ring->xenblkd) {
>                       kthread_stop(ring->xenblkd);
>                       wake_up(&ring->shutdown_wq);
> @@ -296,7 +299,7 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
>               BUG_ON(ring->free_pages_num != 0);
>               BUG_ON(ring->persistent_gnt_c != 0);
>               WARN_ON(i != (XEN_BLKIF_REQS_PER_PAGE * blkif->nr_ring_pages));
> -             xen_blkif_put(blkif);
> +             ring->active = 0;
>       }
>       blkif->nr_ring_pages = 0;
>       /*
> 

-- 
Company details: http://ts.fujitsu.com/imprint.html

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel