[dm-devel] [bug report] dm: add statistics support

[Dan Carpenter]

Gar.  I'm sorry, this is really new code and you're right that it's
buggy.

On Thu, Mar 15, 2018 at 03:25:52PM -0400, Mikulas Patocka wrote:
> > The patch fd2ed4d25270: "dm: add statistics support" from Aug 16,
> > 2013, leads to the following static checker warning:
> > 
> > 	drivers/md/dm-stats.c:371 dm_stats_create()
> > 	warn: dead code because of 's->id == ((~0 >> 1))' and 'tmp_s->id < s->id'
> 
> ((~0 >> 1)) is -1 and we are comparing it against INT_MAX. Perhaps the 
> static checker is buggy because it believes that INT_MAX is -1.
> 
> INT_MAX definition in the linux kernel is ((int)(~0U>>1)).
> 

Yeah, the format of the smatch outputs is bad.  It gets INT_MAX correct
internally it just prints it out badly.  The problem here is that Smatch
is crap at parsing loops.  Parsing seems like an essential thing, but
you'd be surprised how many times you can get away with parsing them
badly.  The main issue is that parsing them correctly is probably a big
slow down because you'd have to go through a lot of code twice...

Anyway, thanks for looking at this and sorry for the noise.

regards,
dan carpenter