linux-kernel - Re: [PATCH] scsi: storvsc: Prevent running tasklet for long

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Message-ID: <1c4bc0cf-6665-3fe6-28d8-8e9613e3f9d4@linux.microsoft.com>
Date:   Wed, 6 Jul 2022 19:59:09 +0530
From:   Praveen Kumar <kumarpraveen@...ux.microsoft.com>
To:     Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, decui@...rosoft.com, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, linux-hyperv@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        ssengar@...rosoft.com, mikelley@...rosoft.com
Subject: Re: [PATCH] scsi: storvsc: Prevent running tasklet for long

On 06-07-2022 15:23, Saurabh Singh Sengar wrote:
> On Wed, Jul 06, 2022 at 02:44:42PM +0530, Praveen Kumar wrote:
>> On 05-07-2022 21:02, Saurabh Sengar wrote:
>>> There can be scenarios where packets in ring buffer are continuously
>>> getting queued from upper layer and dequeued from storvsc interrupt
>>> handler, such scenarios can hold the foreach_vmbus_pkt loop (which is
>>> executing as a tasklet) for a long duration. Theoretically its possible
>>> that this loop executes forever. Add a condition to limit execution of
>>> this tasklet for finite amount of time to avoid such hazardous scenarios.
>>>
>>> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
>>> ---
>>>  drivers/scsi/storvsc_drv.c | 7 +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
>>> index fe000da..0c428cb 100644
>>> --- a/drivers/scsi/storvsc_drv.c
>>> +++ b/drivers/scsi/storvsc_drv.c
>>> @@ -60,6 +60,9 @@
>>>  #define VMSTOR_PROTO_VERSION_WIN8_1	VMSTOR_PROTO_VERSION(6, 0)
>>>  #define VMSTOR_PROTO_VERSION_WIN10	VMSTOR_PROTO_VERSION(6, 2)
>>>  
>>> +/* channel callback timeout in ms */
>>> +#define CALLBACK_TIMEOUT		5
>>
>> If I may, it would be good if we have the CALLBACK_TIMEOUT configurable based upon user's requirement with default value to '5'.
>> I assume, this value '5' fits best to the use-case which we are trying to resolve here. Thanks.
> 
> Agree, how about adding a sysfs entry for this parameter
> 

Sounds good to me. Thanks.

Regards,

~Praveen.