> -----Original Message----- > From: Roger Pau Monné <roger.pau@xxxxxxxxxx> > Sent: 11 December 2019 13:55 > To: Durrant, Paul <pdurrant@xxxxxxxxxx>; Juergen Gross <jgross@xxxxxxxx> > 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 Wed, Dec 11, 2019 at 01:27:42PM +0000, Durrant, Paul wrote: > > > -----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? > > Adjusting on commit would be fine for me, but it's up to Juergen since > he is the one that will pick this up. IIRC the module unload patches > didn't go through the block subsystem. True. I forgot manually add Juergen cc list. Paul > > Thanks, Roger.
