> -----Original Message----- > From: Roger Pau Monné <roger.pau@xxxxxxxxxx> > Sent: 11 December 2019 11:29 > To: Durrant, Paul <pdurrant@xxxxxxxxxx> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; linux-block@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx; Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; > Jens Axboe <axboe@xxxxxxxxx> > Subject: Re: [PATCH] xen-blkback: prevent premature module unload > > 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 <pdurrant@xxxxxxxxxx> > > Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx> > > One nit below. > > > --- > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > > Cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx> > > Cc: Jens Axboe <axboe@xxxxxxxxx> > > --- > > 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 Oh yes. Can this be done on commit, or would you like me to send a v2? Paul > > + */ > > + __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 > >
