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xen-blkback: prevent premature module unload

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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>
This commit is contained in:
Paul Durrant 2019-12-10 14:53:05 +00:00 committed by Juergen Gross
parent 14855954f6
commit fa2ac657f9
1 changed files with 10 additions and 0 deletions
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10
drivers/block/xen-blkback/xenbus.c
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@ -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)