Re: [PATCH 12/13] drivers/staging/unisys/visorhba: convert stats to use seqnum_ops

[Shuah Khan]

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@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   .../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