From fa2ac657f9783f0891b2935490afe9a7fd29d3fa Mon Sep 17 00:00:00 2001 From: Paul Durrant Date: Tue, 10 Dec 2019 14:53:05 +0000 Subject: xen-blkback: prevent premature module unload MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Roger Pau Monné Signed-off-by: Juergen Gross --- drivers/block/xen-blkback/xenbus.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'drivers/block/xen-blkback') diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index e8c5c54e1d26..d6a6adfd5159 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 freed back to the cache. + */ + __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) -- cgit v1.2.3