linux-kernel - Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on transfer failure

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Message-ID: <1245181972.17067189.1417072471636.JavaMail.zimbra@redhat.com>
Date:	Thu, 27 Nov 2014 02:14:31 -0500 (EST)
From:	Jason Wang <jasowang@...hat.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	driverdev-devel@...uxdriverproject.org, olaf@...fle.de,
	apw@...onical.com, kys@...rosoft.com, vkuznets@...hat.com,
	haiyangz@...rosoft.com
Subject: Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on transfer
 failure



----- Original Message -----
> In the case the user-space daemon crashes, hangs or is killed, we
> need to down the semaphore, otherwise, after the daemon starts next
> time, the obsolete data in fcopy_transaction.message or
> fcopy_transaction.fcopy_msg will be used immediately.
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
> 
> v2: I removed the "FCP" prefix as Greg asked.
> 
>     I also updated the output message a little:
>     "FCP: failed to acquire the semaphore" -->
>     "can not acquire the semaphore: it is benign"
> 
>  drivers/hv/hv_fcopy.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
> index 23b2ce2..c518ad9 100644
> --- a/drivers/hv/hv_fcopy.c
> +++ b/drivers/hv/hv_fcopy.c
> @@ -86,6 +86,15 @@ static void fcopy_work_func(struct work_struct *dummy)
>  	 * process the pending transaction.
>  	 */
>  	fcopy_respond_to_host(HV_E_FAIL);
> +
> +	/* In the case the user-space daemon crashes, hangs or is killed, we
> +	 * need to down the semaphore, otherwise, after the daemon starts next
> +	 * time, the obsolete data in fcopy_transaction.message or
> +	 * fcopy_transaction.fcopy_msg will be used immediately.
> +	 */

Looks still racy, what happens if the daemon start before down_trylock()
but after fcopy_respont_to_host() here?

> +	if (down_trylock(&fcopy_transaction.read_sema))
> +		pr_debug("can not acquire the semaphore: it is benign\n");

typo
> +
>  }
>  
>  static int fcopy_handle_handshake(u32 version)
> --
> 1.9.1
> 
> --
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