Messages in this thread | | | Subject | Re: [PATCH] xen-blkback: prevent premature module unload | From | Jürgen Groß <> | Date | Wed, 11 Dec 2019 14:56:54 +0100 |
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On 11.12.19 14:55, Roger Pau Monné wrote: > On Wed, Dec 11, 2019 at 01:27:42PM +0000, Durrant, Paul wrote: >>> -----Original Message----- >>> From: Roger Pau Monné <roger.pau@citrix.com> >>> Sent: 11 December 2019 11:29 >>> To: Durrant, Paul <pdurrant@amazon.com> >>> Cc: xen-devel@lists.xenproject.org; linux-block@vger.kernel.org; linux- >>> kernel@vger.kernel.org; Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>; >>> Jens Axboe <axboe@kernel.dk> >>> 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@amazon.com> >>> >>> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> >>> >>> One nit below. >>> >>>> --- >>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >>>> Cc: "Roger Pau Monné" <roger.pau@citrix.com> >>>> Cc: Jens Axboe <axboe@kernel.dk> >>>> --- >>>> 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.
Oh, right. Yes, will fix this when committing.
Juergen
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