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

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Date:	Thu, 5 Mar 2015 03:06:08 -0500 (EST)
From:	Jason Wang <jasowang@...hat.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	"K. Y. Srinivasan" <kys@...rosoft.com>,
	devel@...uxdriverproject.org,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	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 -----
> 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>

Acked-by: Jason Wang <jasowang@...hat.com>
> ---
> This patch is dependent on the previously posted 'Drivers: hv: hv_balloon:
> eliminate the trylock path in acquire/release_region_mutex'.
> ---
>  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;
>  		}
>  
> --
> 1.9.3
> 
> --
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