linux-kernel - Re: [PATCH v2 1/9] atomic: Prepare scripts for macro ops

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Message-ID: <YbON7H4YwnSzG8z0@FVFF77S0Q05N>
Date:   Fri, 10 Dec 2021 17:27:20 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     will@...nel.org, boqun.feng@...il.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, elver@...gle.com,
        keescook@...omium.org, hch@...radead.org,
        torvalds@...ux-foundation.org, axboe@...nel.dk
Subject: Re: [PATCH v2 1/9] atomic: Prepare scripts for macro ops

On Fri, Dec 10, 2021 at 05:16:19PM +0100, Peter Zijlstra wrote:
> Due to the limited usability of the GCC 'Labels as Values' extention,
> specifically it refuses to have a goto in an __always_inline function,
> even with a compile time constant label pointer, some new atomic ops
> will need to be introduced as macros.
> 
> The xchg/cmpxchg family is already macros so extend that code to the
> regular atomic ops.
> 
> Specifically introduce meta-'M', meta-'m' and meta-'n' to signify the
> op is a macro and add arg-'L', arg-'V' and arg-'P' for Label, VarArg
> and Pair arguments respectively.

Looks like `M` got factored out into the next patch, so I think that can be
deleted from this commit message.

> This unconvered some latent bugs in the instrumentation wrappery,
> specifically the try_cmpxchg() @oldp argument was instrumented as an
> atomic_read_write, while it's a regular read_write and many of the
> gen_xchg() ops had atomic_write instrumentation while
> atomic_read_write seems more appropriate.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/atomic/atomic-instrumented.h |   78 +++++++--------
>  scripts/atomic/atomic-tbl.sh               |    8 +
>  scripts/atomic/atomics.tbl                 |    5 +
>  scripts/atomic/gen-atomic-fallback.sh      |    4 
>  scripts/atomic/gen-atomic-instrumented.sh  |  142 +++++++++++++++++++----------
>  scripts/atomic/gen-atomic-long.sh          |   32 +++++-
>  6 files changed, 177 insertions(+), 92 deletions(-)
> 

[...]

> --- a/scripts/atomic/atomics.tbl
> +++ b/scripts/atomic/atomics.tbl
> @@ -10,12 +10,17 @@
>  # * F/f	- fetch: returns base type (has fetch_ variants)
>  # * l	- load: returns base type (has _acquire order variant)
>  # * s	- store: returns void (has _release order variant)
> +# * m	- macro: with return value
> +# * n	- macro: with No return value
>  #
>  # Where args contains list of type[:name], where type is:
>  # * cv	- const pointer to atomic base type (atomic_t/atomic64_t/atomic_long_t)
>  # * v	- pointer to atomic base type (atomic_t/atomic64_t/atomic_long_t)
> +# * P	- pointer to pair of atomic base type
>  # * i	- base type (int/s64/long)
>  # * p	- pointer to base type (int/s64/long)
> +# * L	- label for exception case
> +# * V:... - vararg

Nit: should've been a tab here?

[...]

> @@ -51,57 +112,49 @@ gen_proto_order_variant()
>  	local order="$1"; shift
>  	local atomic="$1"; shift
>  	local int="$1"; shift
> +	local atomicname;
>  
> -	local atomicname="${atomic}_${pfx}${name}${sfx}${order}"
> +	if [ -n "${atomic}" ]; then
> +		atomicname="${atomic}_${pfx}${name}${sfx}${order}"
> +	else
> +		atomicname="${pfx}${name}${sfx}${order}"
> +	fi

How about:

	local atomicname="${pfx}${name}${sfx}${order}"
	if [ -n "${atomic}" ]; then
		atomicname="${atomic}_${atomicname}"
	fi

... so that it's clear we're just adding the atomic type as a prefix, and the
rest of the name should be the same either way?

Regardless of that specifically:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.