linux-kernel - Re: [PATCH] block: Annotate a racy read in blk_do_io

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Date: Mon, 20 May 2024 11:05:31 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Marco Elver <elver@...gle.com>
Cc: Bart Van Assche <bvanassche@....org>, Breno Leitao <leitao@...ian.org>,
	Jens Axboe <axboe@...nel.dk>,
	"open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: Annotate a racy read in blk_do_io_stat()

On Thu, May 16, 2024 at 08:35:02AM +0200, Marco Elver wrote:
> On Wed, 15 May 2024 at 23:51, Paul E. McKenney <paulmck@...nel.org> wrote:
> [...]
> > > And I just checked the current access-marking.txt to see where we
> > > might add more, and found the section "ACCESS-DOCUMENTATION OPTIONS"
> > > already exists. I think that section is perfectly reasonable as is,
> > > and it does explicitly talk about ASSERT_EXCLUSIVE* macros.
> > >
> > > Did you want to add it more prominently at the top? If so, maybe a
> > > brief forward-reference to that section might be helpful.
> >
> > How about like this?
> >
> > ------------------------------------------------------------------------
> >
> > The Linux kernel provides the following access-marking options:
> >
> > 1.      Plain C-language accesses (unmarked), for example, "a = b;"
> >
> > 2.      Data-race marking, for example, "data_race(a = b);"
> >
> > 3.      READ_ONCE(), for example, "a = READ_ONCE(b);"
> >         The various forms of atomic_read() also fit in here.
> >
> > 4.      WRITE_ONCE(), for example, "WRITE_ONCE(a, b);"
> >         The various forms of atomic_set() also fit in here.
> >
> > 5.      __data_racy, for example "int __data_racy a;"
> >
> > 6.      KCSAN's negative-marking assertions, ASSERT_EXCLUSIVE_ACCESS()
> >         and ASSERT_EXCLUSIVE_WRITER(), are desccribed in the
> >         "ACCESS-DOCUMENTATION OPTIONS" section below.
> 
> s/desccribed/described/

Good eyes, fixed!

> > ------------------------------------------------------------------------
> >
> > Would that work?
> 
> It works for me, if we agree that "negative marking" makes sense: if
> the other markings indicate the access is happening concurrently with
> others, a negative marking does the opposite.

Very good, I will send this out shortly after v6.10-rc1 comes out and
let's see where the bikeshedding leads.  ;-)

							Thanx, Paul