linux-kernel - RE: [PATCH 1/1] Drivers: hv: hv_util: Avoid dynamic allocation in time synch

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Date:   Fri, 16 Sep 2016 14:13:26 +0000
From:   KY Srinivasan <kys@...rosoft.com>
To:     KY Srinivasan <kys@...rosoft.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "leann.ogasawara@...onical.com" <leann.ogasawara@...onical.com>
CC:     Vivek Yadav <vyadav@...rosoft.com>
Subject: RE: [PATCH 1/1] Drivers: hv: hv_util: Avoid dynamic allocation in
 time synch



> -----Original Message-----
> From: kys@...hange.microsoft.com [mailto:kys@...hange.microsoft.com]
> Sent: Friday, September 16, 2016 9:31 PM
> To: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> vkuznets@...hat.com; jasowang@...hat.com;
> leann.ogasawara@...onical.com
> Cc: Vivek Yadav <vyadav@...rosoft.com>; KY Srinivasan
> <kys@...rosoft.com>
> Subject: [PATCH 1/1] Drivers: hv: hv_util: Avoid dynamic allocation in time
> synch
> 
> From: Vivek yadav <vyadav@...rosoft.com>
> 
> Under stress, we have seen allocation failure in time synch code. Avoid
> this dynamic allocation.
> 
> Signed-off-by: Vivek Yadav <vyadav@...rosoft.com>
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>

Greg, 
Please ignore this patch, It is already committed and got sent because of a glitch.

Regards,

K. Y
> ---
>  drivers/hv/hv_util.c |   39 ++++++++++++++++++++++++++++-----------
>  1 files changed, 28 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
> index 6286bdc..4aa3cb6 100644
> --- a/drivers/hv/hv_util.c
> +++ b/drivers/hv/hv_util.c
> @@ -64,9 +64,14 @@ static struct hv_util_service util_shutdown = {
>  	.util_cb = shutdown_onchannelcallback,
>  };
> 
> +static int hv_timesync_init(struct hv_util_service *srv);
> +static void hv_timesync_deinit(void);
> +
>  static void timesync_onchannelcallback(void *context);
>  static struct hv_util_service util_timesynch = {
>  	.util_cb = timesync_onchannelcallback,
> +	.util_init = hv_timesync_init,
> +	.util_deinit = hv_timesync_deinit,
>  };
> 
>  static void heartbeat_onchannelcallback(void *context);
> @@ -201,7 +206,6 @@ static void hv_set_host_time(struct work_struct
> *work)
>  	host_ts = ns_to_timespec(host_tns);
> 
>  	do_settimeofday(&host_ts);
> -	kfree(wrk);
>  }
> 
>  /*
> @@ -217,22 +221,24 @@ static void hv_set_host_time(struct work_struct
> *work)
>   * typically used as a hint to the guest. The guest is under no obligation
>   * to discipline the clock.
>   */
> +static struct adj_time_work  wrk;
>  static inline void adj_guesttime(u64 hosttime, u64 reftime, u8 flags)
>  {
> -	struct adj_time_work    *wrk;
> 
> -	wrk = kmalloc(sizeof(struct adj_time_work), GFP_ATOMIC);
> -	if (wrk == NULL)
> +	/*
> +	 * This check is safe since we are executing in the
> +	 * interrupt context and time synch messages arre always
> +	 * delivered on the same CPU.
> +	 */
> +	if (work_pending(&wrk.work))
>  		return;
> 
> -	wrk->host_time = hosttime;
> -	wrk->ref_time = reftime;
> -	wrk->flags = flags;
> +	wrk.host_time = hosttime;
> +	wrk.ref_time = reftime;
> +	wrk.flags = flags;
>  	if ((flags & (ICTIMESYNCFLAG_SYNC | ICTIMESYNCFLAG_SAMPLE)) !=
> 0) {
> -		INIT_WORK(&wrk->work, hv_set_host_time);
> -		schedule_work(&wrk->work);
> -	} else
> -		kfree(wrk);
> +		schedule_work(&wrk.work);
> +	}
>  }
> 
>  /*
> @@ -457,6 +463,17 @@ static  struct hv_driver util_drv = {
>  	.remove =  util_remove,
>  };
> 
> +static int hv_timesync_init(struct hv_util_service *srv)
> +{
> +	INIT_WORK(&wrk.work, hv_set_host_time);
> +	return 0;
> +}
> +
> +static void hv_timesync_deinit(void)
> +{
> +	cancel_work_sync(&wrk.work);
> +}
> +
>  static int __init init_hyperv_utils(void)
>  {
>  	pr_info("Registering HyperV Utility Driver\n");
> --
> 1.7.4.1