linux-kernel - Re: [PATCH 12/13] drivers/staging/unisys/visorhba: convert stats to use seqnum

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Date:   Tue, 10 Nov 2020 14:02:14 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     david.kershner@...sys.com, keescook@...omium.org,
        peterz@...radead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 12/13] drivers/staging/unisys/visorhba: convert stats to
 use seqnum_ops

On 11/10/20 1:42 PM, Greg KH wrote:
> On Tue, Nov 10, 2020 at 12:53:38PM -0700, Shuah Khan wrote:
>> seqnum_ops api is introduced to be used when a variable is used as
>> a sequence/stat counter and doesn't guard object lifetimes. This
>> clearly differentiates atomic_t usages that guard object lifetimes.
>>
>> seqnum32 variables wrap around to INT_MIN when it overflows and
>> should not be used to guard resource lifetimes, device usage and
>> open counts that control state changes, and pm states.
>>
>> atomic_t variables used for error_count and ios_threshold are atomic
>> counters and guarded by max. values. No change to the behavior with
>> this change.
>>
>> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
>> ---
>>   .../staging/unisys/visorhba/visorhba_main.c   | 37 ++++++++++---------
>>   1 file changed, 19 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/staging/unisys/visorhba/visorhba_main.c b/drivers/staging/unisys/visorhba/visorhba_main.c
>> index 7ae5306b92fe..3209958b8aaa 100644
>> --- a/drivers/staging/unisys/visorhba/visorhba_main.c
>> +++ b/drivers/staging/unisys/visorhba/visorhba_main.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/module.h>
>>   #include <linux/seq_file.h>
>>   #include <linux/visorbus.h>
>> +#include <linux/seqnum_ops.h>
>>   #include <scsi/scsi.h>
>>   #include <scsi/scsi_host.h>
>>   #include <scsi/scsi_cmnd.h>
>> @@ -41,8 +42,8 @@ MODULE_ALIAS("visorbus:" VISOR_VHBA_CHANNEL_GUID_STR);
>>   struct visordisk_info {
>>   	struct scsi_device *sdev;
>>   	u32 valid;
>> -	atomic_t ios_threshold;
>> -	atomic_t error_count;
>> +	struct seqnum32 ios_threshold;
>> +	struct seqnum32 error_count;
> 
> Are you sure the threshold variable is a sequence number >
> It goes up and down, not just up and up and up.

Right. I does go down. Turns out this is the only place seqnum32_dec()
is used. :)

I will fix. I noticed you made a comment about _dec() interfaces on
1/13. I can drop those as well. This way seqnum_ops can be just used
for up counters.

thanks,
-- Shuah