[PATCH] Drivers: hv: hv_fcopy: fix a race condition for SMP guest

[PATCH] Drivers: hv: hv_fcopy: fix a race condition for SMP guest

[Dexuan Cui]

We should schedule the 5s "timer work" before starting the data transfer,
otherwise, the data transfer code may finish so fast on another
virtual cpu that when the code(fcopy_write()) trying to cancel the 5s
"timer work" can occasionally fail because the "timer work" may haven't
been scheduled yet and as a result the fcopy process will be aborted
wrongly by fcopy_work_func() in 5s.

Thank Liz Zhang <lizzha@microsoft.com> for the initial investigation
on the bug.

This addresses https://bugzilla.redhat.com/show_bug.cgi?id=1118123

Tested-by: Liz Zhang <lizzha@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/hv/hv_fcopy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index eaaa3d8..23b2ce2 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -246,8 +246,8 @@ void hv_fcopy_onchannelcallback(void *context)
 		/*
 		 * Send the information to the user-level daemon.
 		 */
-		fcopy_send_data();
 		schedule_delayed_work(&fcopy_work, 5*HZ);
+		fcopy_send_data();
 		return;
 	}
 	icmsghdr->icflags = ICMSGHDRFLAG_TRANSACTION | ICMSGHDRFLAG_RESPONSE;
-- 
1.9.1

RE: [PATCH] Drivers: hv: hv_fcopy: fix a race condition for SMP guest

[KY Srinivasan]

> -----Original Message-----
> From: Dexuan Cui [mailto:decui@microsoft.com]
> Sent: Wednesday, July 16, 2014 12:01 AM
> To: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org; driverdev-
> devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com;
> jasowang@redhat.com
> Cc: KY Srinivasan; Haiyang Zhang
> Subject: [PATCH] Drivers: hv: hv_fcopy: fix a race condition for SMP guest
> 
> We should schedule the 5s "timer work" before starting the data transfer,
> otherwise, the data transfer code may finish so fast on another virtual cpu
> that when the code(fcopy_write()) trying to cancel the 5s "timer work" can
> occasionally fail because the "timer work" may haven't been scheduled yet
> and as a result the fcopy process will be aborted wrongly by
> fcopy_work_func() in 5s.
> 
> Thank Liz Zhang <lizzha@microsoft.com> for the initial investigation on the
> bug.
> 
> This addresses https://bugzilla.redhat.com/show_bug.cgi?id=1118123
> 
> Tested-by: Liz Zhang <lizzha@microsoft.com>
> Cc: K. Y. Srinivasan <kys@microsoft.com>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Dexuan Cui <decui@microsoft.com>

Thanks Dexuan.
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>


K. Y

> ---
>  drivers/hv/hv_fcopy.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c index
> eaaa3d8..23b2ce2 100644
> --- a/drivers/hv/hv_fcopy.c
> +++ b/drivers/hv/hv_fcopy.c
> @@ -246,8 +246,8 @@ void hv_fcopy_onchannelcallback(void *context)
>  		/*
>  		 * Send the information to the user-level daemon.
>  		 */
> -		fcopy_send_data();
>  		schedule_delayed_work(&fcopy_work, 5*HZ);
> +		fcopy_send_data();
>  		return;
>  	}
>  	icmsghdr->icflags = ICMSGHDRFLAG_TRANSACTION |
> ICMSGHDRFLAG_RESPONSE;
> --
> 1.9.1