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From: Yury Norov <yury.norov@gmail.com>
To: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	lizefan@huawei.com, Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	josh@joshtriplett.org, Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	fweisbec@gmail.com, Rasmus Villemoes <linux@rasmusvillemoes.dk>
Subject: Re: [PATCH 3/8] lib: bitmap: fold nbits into region struct
Date: Wed, 27 Jan 2021 16:47:50 -0800	[thread overview]
Message-ID: <CAAH8bW-tWRJ4m3pP37YBVrferOa9CwMZGdZkSDC+GXvBfC=Uhw@mail.gmail.com> (raw)
In-Reply-To: <20210127080206.GE23530@windriver.com>

On Wed, Jan 27, 2021 at 12:02 AM Paul Gortmaker
<paul.gortmaker@windriver.com> wrote:
>
> [Re: [PATCH 3/8] lib: bitmap: fold nbits into region struct] On 26/01/2021 (Tue 23:16) Andy Shevchenko wrote:
>
> > On Tue, Jan 26, 2021 at 12:11:36PM -0500, Paul Gortmaker wrote:
> > > This will reduce parameter passing and enable using nbits as part
> > > of future dynamic region parameter parsing.
> >
> > One nit below, nevertheless
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> >
> > > Cc: Yury Norov <yury.norov@gmail.com>
> > > Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > Suggested-by: Yury Norov <yury.norov@gmail.com>
> > > Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
> > > ---
> > >  lib/bitmap.c | 19 ++++++++++---------
> > >  1 file changed, 10 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/lib/bitmap.c b/lib/bitmap.c
> > > index 75006c4036e9..162e2850c622 100644
> > > --- a/lib/bitmap.c
> > > +++ b/lib/bitmap.c
> > > @@ -487,24 +487,24 @@ EXPORT_SYMBOL(bitmap_print_to_pagebuf);
> > >
> > >  /*
> > >   * Region 9-38:4/10 describes the following bitmap structure:
> > > - * 0          9  12    18                  38
> > > - * .........****......****......****......
> > > - *     ^  ^     ^                   ^
> > > - *      start  off   group_len            end
> > > + * 0          9  12    18                  38           N
> > > + * .........****......****......****..................
> > > + *     ^  ^     ^                   ^           ^
> > > + *      start  off   group_len            end       nbits
> > >   */
> > >  struct region {
> > >     unsigned int start;
> > >     unsigned int off;
> > >     unsigned int group_len;
> > >     unsigned int end;
> > > +   unsigned int nbits;
> > >  };
> > >
> > > -static int bitmap_set_region(const struct region *r,
> > > -                           unsigned long *bitmap, int nbits)
> > > +static int bitmap_set_region(const struct region *r, unsigned long *bitmap)
> > >  {
> > >     unsigned int start;
> > >
> > > -   if (r->end >= nbits)
> > > +   if (r->end >= r->nbits)
> > >             return -ERANGE;
> > >
> > >     for (start = r->start; start <= r->end; start += r->group_len)
> > > @@ -640,7 +640,8 @@ int bitmap_parselist(const char *buf, unsigned long *maskp, int nmaskbits)
> > >     struct region r;
> > >     long ret;
> > >
> > > -   bitmap_zero(maskp, nmaskbits);
> > > +   r.nbits = nmaskbits;
> >
> > > +   bitmap_zero(maskp, r.nbits);
> >
> > This sounds not right from style perspective.
> > You have completely uninitialized r on stack, then you assign only one value
> > for immediate use here and...
>
> So, this change was added because Yury suggested that I "..store
> nmaskbits in the struct region, and avoid passing nmaskbits as a
> parameter."
>
> To which I originally noted "I considered that and went with the param
> so as to not open the door to someone possibly using an uninitialized
> struct value later."

struct region is purely internal structure. It's declared on stack and filled
field-by-field using helpers. 'Someone' misusing the structure doesn't exist
because the structure doesn't exist out of the scope.

> https://lore.kernel.org/lkml/20210122044357.GS16838@windriver.com/
>
> Looking back, I had a similar thought as to yours, it seems...
>
> I am also thinking more and more that nbits doesn't belong in the
> region anyway - yes, a region gets validated against a specific nbits
> eventually, but it doesn't need an nbits field to be a complete
> specification.  The region "0-3" is a complete specification for "the
> 1st four cores" and is as valid on a 4 core machine as it is on a 64 core
> machine -- a validation we do when we deploy the region on that machine.
>
> I will set this change aside and get the nbits value to getnum() another
> way, and leave the region struct as it was -- without a nbits field.
>
> This will also resolve having the macro handling of region that you were
> not really liking.
>
> Paul.

Region is a convenient structure. Adding nbits into it helps to remove
validation
logic from bitmap_set_region(), so it's worth doing this.

Can you please have it unchanged?

Thanks,
Yury

  reply	other threads:[~2021-01-28  0:49 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-26 17:11 [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Paul Gortmaker
2021-01-26 17:11 ` [PATCH 1/8] lib: test_bitmap: clearly separate ERANGE from EINVAL tests Paul Gortmaker
2021-01-26 21:04   ` Andy Shevchenko
2021-01-27  7:21     ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 2/8] lib: test_bitmap: add more start-end:offset/len tests Paul Gortmaker
2021-01-26 21:11   ` Andy Shevchenko
2021-01-27  3:03   ` Yury Norov
2021-01-26 17:11 ` [PATCH 3/8] lib: bitmap: fold nbits into region struct Paul Gortmaker
2021-01-26 21:16   ` Andy Shevchenko
2021-01-26 21:18     ` Andy Shevchenko
2021-01-27  8:02     ` Paul Gortmaker
2021-01-28  0:47       ` Yury Norov [this message]
2021-01-28 10:17         ` Andy Shevchenko
2021-01-27  3:08   ` Yury Norov
2021-01-26 17:11 ` [PATCH 4/8] lib: bitmap: move ERANGE check from set_region to check_region Paul Gortmaker
2021-01-26 21:19   ` Andy Shevchenko
2021-01-27  3:12   ` Yury Norov
2021-01-26 17:11 ` [PATCH 5/8] lib: bitmap_getnum: separate arg into region and field Paul Gortmaker
2021-01-26 21:23   ` Andy Shevchenko
2021-01-27  2:58     ` Yury Norov
2021-01-27  8:38       ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-01-26 21:37   ` Andy Shevchenko
2021-01-26 21:41     ` Andy Shevchenko
2021-01-27 17:57       ` Yury Norov
2021-01-27  8:20     ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 7/8] lib: test_bitmap: add tests for "N" alias Paul Gortmaker
2021-01-26 17:11 ` [PATCH 8/8] rcu: deprecate "all" option to rcu_nocbs= Paul Gortmaker
2021-01-26 21:36   ` Yury Norov
2021-01-26 22:17     ` Paul E. McKenney
2021-01-26 22:27 ` [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Yury Norov
2021-01-27  9:12   ` Paul Gortmaker

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