linux-kernel - Re: [PATCH 2/4] Drivers: hv: vmbus: avoid wait_for

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Date:	Mon, 15 Feb 2016 22:00:21 +0100
From:	Radim Krcmar <rkrcmar@...hat.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:	devel@...uxdriverproject.org, linux-kernel@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Cathy Avery <cavery@...hat.com>
Subject: Re: [PATCH 2/4] Drivers: hv: vmbus: avoid wait_for_completion() on
 crash

2016-02-12 16:42+0100, Vitaly Kuznetsov:
> wait_for_completion() may sleep, it enables interrupts and this
> is something we really want to avoid on crashes because interrupt
> handlers can cause other crashes. Switch to the recently introduced
> vmbus_wait_for_unload() doing busy wait instead.

(Too bad we fix crashers, so there is nothing to test on. :])

> Reported-by: Radim Krcmar <rkrcmar@...hat.com>

Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>

> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  drivers/hv/channel_mgmt.c | 4 ++--
>  drivers/hv/connection.c   | 2 +-
>  drivers/hv/hyperv_vmbus.h | 2 +-
>  drivers/hv/vmbus_drv.c    | 4 ++--
>  4 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 763d0c1..bd60207 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -556,7 +556,7 @@ static void vmbus_unload_response(struct vmbus_channel_message_header *hdr)
>  	complete(&vmbus_connection.unload_event);
>  }
>  
> -void vmbus_initiate_unload(void)
> +void vmbus_initiate_unload(bool crash)
>  {
>  	struct vmbus_channel_message_header hdr;
>  
> @@ -573,7 +573,7 @@ void vmbus_initiate_unload(void)
>  	 * vmbus_initiate_unload() is also called on crash and the crash can be
>  	 * happening in an interrupt context, where scheduling is impossible.
>  	 */
> -	if (!in_interrupt())
> +	if (!crash)
>  		wait_for_completion(&vmbus_connection.unload_event);
>  	else
>  		vmbus_wait_for_unload();
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 3dc5a9c..fb63d30 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -236,7 +236,7 @@ void vmbus_disconnect(void)
>  	/*
>  	 * First send the unload request to the host.
>  	 */
> -	vmbus_initiate_unload();
> +	vmbus_initiate_unload(false);
>  
>  	if (vmbus_connection.work_queue) {
>  		drain_workqueue(vmbus_connection.work_queue);
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
> index 4ebc796..e6160a0 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -665,7 +665,7 @@ void hv_vss_onchannelcallback(void *);
>  int hv_fcopy_init(struct hv_util_service *);
>  void hv_fcopy_deinit(void);
>  void hv_fcopy_onchannelcallback(void *);
> -void vmbus_initiate_unload(void);
> +void vmbus_initiate_unload(bool crash);
>  
>  static inline void hv_poll_channel(struct vmbus_channel *channel,
>  				   void (*cb)(void *))
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 895eeed..08f98a1 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -1266,7 +1266,7 @@ static void hv_kexec_handler(void)
>  	int cpu;
>  
>  	hv_synic_clockevents_cleanup();
> -	vmbus_initiate_unload();
> +	vmbus_initiate_unload(false);
>  	for_each_online_cpu(cpu)
>  		smp_call_function_single(cpu, hv_synic_cleanup, NULL, 1);
>  	hv_cleanup();
> @@ -1274,7 +1274,7 @@ static void hv_kexec_handler(void)
>  
>  static void hv_crash_handler(struct pt_regs *regs)
>  {
> -	vmbus_initiate_unload();
> +	vmbus_initiate_unload(true);
>  	/*
>  	 * In crash handler we can't schedule synic cleanup for all CPUs,
>  	 * doing the cleanup for current CPU only. This should be sufficient
> -- 
> 2.5.0
>