On Tue, Dec 10, 2019 at 02:53:05PM +0000, Paul Durrant wrote:
> Objects allocated by xen_blkif_alloc come from the 'blkif_cache' kmem
> cache. This cache is destoyed when xen-blkif is unloaded so it is
> necessary to wait for the deferred free routine used for such objects to
> complete. This necessity was missed in commit 14855954f636 "xen-blkback:
> allow module to be cleanly unloaded". This patch fixes the problem by
> taking/releasing extra module references in xen_blkif_alloc/free()
> respectively.
>
> Signed-off-by: Paul Durrant <pdurr...@amazon.com>
Reviewed-by: Roger Pau Monné <roger....@citrix.com>
One nit below.
> ---
> Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
> Cc: "Roger Pau Monné" <roger....@citrix.com>
> Cc: Jens Axboe <ax...@kernel.dk>
> ---
> drivers/block/xen-blkback/xenbus.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/block/xen-blkback/xenbus.c
> b/drivers/block/xen-blkback/xenbus.c
> index e8c5c54e1d26..59d576d27ca7 100644
> --- a/drivers/block/xen-blkback/xenbus.c
> +++ b/drivers/block/xen-blkback/xenbus.c
> @@ -171,6 +171,15 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid)
> blkif->domid = domid;
> atomic_set(&blkif->refcnt, 1);
> init_completion(&blkif->drain_complete);
> +
> + /*
> + * Because freeing back to the cache may be deferred, it is not
> + * safe to unload the module (and hence destroy the cache) until
> + * this has completed. To prevent premature unloading, take an
> + * extra module reference here and release only when the object
> + * has been free back to the cache.
^ freed
> + */
> + __module_get(THIS_MODULE);
> INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
>
> return blkif;
> @@ -320,6 +329,7 @@ static void xen_blkif_free(struct xen_blkif *blkif)
>
> /* Make sure everything is drained before shutting down */
> kmem_cache_free(xen_blkif_cachep, blkif);
> + module_put(THIS_MODULE);
> }
>
> int __init xen_blkif_interface_init(void)
> --
> 2.20.1
>
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