This is a note to let you know that I've just added the patch titled
xen-blkback: prevent premature module unload
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-blkback-prevent-premature-module-unload.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f9f424f25ba8de9aabb772273ced24015ef39c2e
Author: Paul Durrant <pdurrant@xxxxxxxxxx>
Date: Tue Dec 10 14:53:05 2019 +0000
xen-blkback: prevent premature module unload
[ 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@xxxxxxxxxx>
Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 55869b362fdf..25c41ce070a7 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -179,6 +179,15 @@ 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;
@@ -328,6 +337,7 @@ 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)
