linux-kernel - RE: [PATCH] Drivers: hv: hv_balloon: keep locks balanced on add

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Date:	Sat, 7 Mar 2015 00:35:47 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"Haiyang Zhang" <haiyangz@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dexuan Cui <decui@...rosoft.com>
Subject: RE: [PATCH] Drivers: hv: hv_balloon: keep locks balanced on
 add_memory() failure



> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Monday, March 2, 2015 2:34 AM
> To: KY Srinivasan
> Cc: devel@...uxdriverproject.org; Haiyang Zhang; linux-
> kernel@...r.kernel.org; Dexuan Cui
> Subject: Re: [PATCH] Drivers: hv: hv_balloon: keep locks balanced on
> add_memory() failure
> 
> Vitaly Kuznetsov <vkuznets@...hat.com> writes:
> 
> > When add_memory() fails the following BUG is observed:
> > [  743.646107] hv_balloon: hot_add memory failed error is -17 [
> > 743.679973] [  743.680930] =====================================
> > [  743.680930] [ BUG: bad unlock balance detected! ] [  743.680930]
> > 3.19.0-rc5_bug1131426+ #552 Not tainted [  743.680930]
> > -------------------------------------
> > [  743.680930] kworker/0:2/255 is trying to release lock
> (&dm_device.ha_region_mutex) at:
> > [  743.680930] [<ffffffff81aae5fe>] mutex_unlock+0xe/0x10 [
> > 743.680930] but there are no more locks to release!
> >
> > This happens as we don't acquire ha_region_mutex and hot_add_req()
> > expects us to as it does unconditional mutex_unlock(). Acquire the lock on
> the error path.
> >
> > Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> > ---
> > This patch is dependent on the previously posted 'Drivers: hv: hv_balloon:
> > eliminate the trylock path in acquire/release_region_mutex'.
> 
> Hi K.Y.,
> 
> I don't see this patch in your '[PATCH 0/7] Drivers: hv: Collection fixes and
> enhancements' sent to Greg. Please let me know if you see any issues with it
> as it looks like a pretty important bugfix to me.

Yes, I am sending this patch out soon.

K. Y
> 
> Thanks,
> 
> > ---
> >  drivers/hv/hv_balloon.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index
> > 1283035..771bf84 100644
> > --- a/drivers/hv/hv_balloon.c
> > +++ b/drivers/hv/hv_balloon.c
> > @@ -654,6 +654,7 @@ static void hv_mem_hot_add(unsigned long start,
> > unsigned long size,  }  has->ha_end_pfn -= HA_CHUNK;
> > has->covered_end_pfn -=  processed_pfn;
> > +mutex_lock(&dm_device.ha_region_mutex);
> >  break;
> >  }
> 
> --
>   Vitaly

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