From: Paul Durrant pdurrant@amazon.com
[ Upstream commit fa2ac657f9783f0891b2935490afe9a7fd29d3fa ]
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 pdurrant@amazon.com Reviewed-by: Roger Pau Monné roger.pau@citrix.com Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ed4e80779124..e9fa4a1fc791 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -178,6 +178,15 @@ 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 freed back to the cache. + */ + __module_get(THIS_MODULE); INIT_WORK(&blkif->free_work, xen_blkif_deferred_free);
return blkif; @@ -327,6 +336,7 @@ 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)