Commit ad811070 authored by Mark Rutland's avatar Mark Rutland Committed by Peter Zijlstra
Browse files

locking/atomic: scripts: generate kerneldoc comments 



Currently the atomics are documented in Documentation/atomic_t.txt, and
have no kerneldoc comments. There are a sufficient number of gotchas
(e.g. semantics, noinstr-safety) that it would be nice to have comments
to call these out, and it would be nice to have kerneldoc comments such
that these can be collated.

While it's possible to derive the semantics from the code, this can be
painful given the amount of indirection we currently have (e.g. fallback
paths), and it's easy to be mislead by naming, e.g.

* The unconditional void-returning ops *only* have relaxed variants
  without a _relaxed suffix, and can easily be mistaken for being fully
  ordered.

  It would be nice to give these a _relaxed() suffix, but this would
  result in significant churn throughout the kernel.

* Our naming of conditional and unconditional+test ops is rather
  inconsistent, and it can be difficult to derive the name of an
  operation, or to identify where an op is conditional or
  unconditional+test.

  Some ops are clearly conditional:
  - dec_if_positive
  - add_unless
  - dec_unless_positive
  - inc_unless_negative

  Some ops are clearly unconditional+test:
  - sub_and_test
  - dec_and_test
  - inc_and_test

  However, what exactly those test is not obvious. A _test_zero suffix
  might be clearer.

  Others could be read ambiguously:
  - inc_not_zero	// conditional
  - add_negative	// unconditional+test

  It would probably be worth renaming these, e.g. to inc_unless_zero and
  add_test_negative.

As a step towards making this more consistent and easier to understand,
this patch adds kerneldoc comments for all generated *atomic*_*()
functions. These are generated from templates, with some common text
shared, making it easy to extend these in future if necessary.

I've tried to make these as consistent and clear as possible, and I've
deliberately ensured:

* All ops have their ordering explicitly mentioned in the short and long
  description.

* All test ops have "test" in their short description.

* All ops are described as an expression using their usual C operator.
  For example:

  andnot: "Atomically updates @v to (@v & ~@i)"
  inc:    "Atomically updates @v to (@v + 1)"

  Which may be clearer to non-naative English speakers, and allows all
  the operations to be described in the same style.

* All conditional ops have their condition described as an expression
  using the usual C operators. For example:

  add_unless: "If (@v != @u), atomically updates @v to (@v + @i)"
  cmpxchg:    "If (@v == @old), atomically updates @v to @new"

  Which may be clearer to non-naative English speakers, and allows all
  the operations to be described in the same style.

* All bitwise ops (and,andnot,or,xor) explicitly mention that they are
  bitwise in their short description, so that they are not mistaken for
  performing their logical equivalents.

* The noinstr safety of each op is explicitly described, with a
  description of whether or not to use the raw_ form of the op.

There should be no functional change as a result of this patch.

Reported-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230605070124.3741859-26-mark.rutland@arm.com
parent 8aaf297a

include/linux/atomic/atomic-arch-fallback.h

+1847 −1

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include/linux/atomic/atomic-instrumented.h

+2770 −1

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include/linux/atomic/atomic-long.h

+924 −1

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scripts/atomic/atomic-tbl.sh

+108 −4
Original line number Diff line number Diff line
@@ -36,9 +36,16 @@ meta_has_relaxed() 
	meta_in "$1" "BFIR"

}



#find_fallback_template(pfx, name, sfx, order)

find_fallback_template()

#meta_is_implicitly_relaxed(meta)

meta_is_implicitly_relaxed()

{

	meta_in "$1" "vls"

}



#find_template(tmpltype, pfx, name, sfx, order)

find_template()

{

	local tmpltype="$1"; shift

	local pfx="$1"; shift

	local name="$1"; shift

	local sfx="$1"; shift
@@ -52,8 +59,8 @@ find_fallback_template() 
	#

	# Start at the most specific, and fall back to the most general. Once

	# we find a specific fallback, don't bother looking for more.

	for base in "${pfx}${name}${sfx}${order}" "${name}"; do

		file="${ATOMICDIR}/fallbacks/${base}"

	for base in "${pfx}${name}${sfx}${order}" "${pfx}${name}${sfx}" "${name}"; do

		file="${ATOMICDIR}/${tmpltype}/${base}"



		if [ -f "${file}" ]; then

			printf "${file}"
@@ -62,6 +69,18 @@ find_fallback_template() 
	done

}



#find_fallback_template(pfx, name, sfx, order)

find_fallback_template()

{

	find_template "fallbacks" "$@"

}



#find_kerneldoc_template(pfx, name, sfx, order)

find_kerneldoc_template()

{

	find_template "kerneldoc" "$@"

}



#gen_ret_type(meta, int)

gen_ret_type() {

	local meta="$1"; shift
@@ -142,6 +161,91 @@ gen_args() 
	done

}



#gen_desc_return(meta)

gen_desc_return()

{

	local meta="$1"; shift



	case "${meta}" in

	[v])

		printf "Return: Nothing."

		;;

	[Ff])

		printf "Return: The original value of @v."

		;;

	[R])

		printf "Return: The updated value of @v."

		;;

	[l])

		printf "Return: The value of @v."

		;;

	esac

}



#gen_template_kerneldoc(template, class, meta, pfx, name, sfx, order, atomic, int, args...)

gen_template_kerneldoc()

{

	local template="$1"; shift

	local class="$1"; shift

	local meta="$1"; shift

	local pfx="$1"; shift

	local name="$1"; shift

	local sfx="$1"; shift

	local order="$1"; shift

	local atomic="$1"; shift

	local int="$1"; shift



	local atomicname="${atomic}_${pfx}${name}${sfx}${order}"



	local ret="$(gen_ret_type "${meta}" "${int}")"

	local retstmt="$(gen_ret_stmt "${meta}")"

	local params="$(gen_params "${int}" "${atomic}" "$@")"

	local args="$(gen_args "$@")"

	local desc_order=""

	local desc_instrumentation=""

	local desc_return=""



	if [ ! -z "${order}" ]; then

		desc_order="${order##_}"

	elif meta_is_implicitly_relaxed "${meta}"; then

		desc_order="relaxed"

	else

		desc_order="full"

	fi



	if [ -z "${class}" ]; then

		desc_noinstr="Unsafe to use in noinstr code; use raw_${atomicname}() there."

	else

		desc_noinstr="Safe to use in noinstr code; prefer ${atomicname}() elsewhere."

	fi



	desc_return="$(gen_desc_return "${meta}")"



	. ${template}

}



#gen_kerneldoc(class, meta, pfx, name, sfx, order, atomic, int, args...)

gen_kerneldoc()

{

	local class="$1"; shift

	local meta="$1"; shift

	local pfx="$1"; shift

	local name="$1"; shift

	local sfx="$1"; shift

	local order="$1"; shift



	local atomicname="${atomic}_${pfx}${name}${sfx}${order}"



	local tmpl="$(find_kerneldoc_template "${pfx}" "${name}" "${sfx}" "${order}")"

	if [ -z "${tmpl}" ]; then

		printf "/*\n"

		printf " * No kerneldoc available for ${class}${atomicname}\n"

		printf " */\n"

	else

	gen_template_kerneldoc "${tmpl}" "${class}" "${meta}" "${pfx}" "${name}" "${sfx}" "${order}" "$@"

	fi

}



#gen_proto_order_variants(meta, pfx, name, sfx, ...)

gen_proto_order_variants()

{

scripts/atomic/gen-atomic-fallback.sh

+2 −0
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ gen_proto_order_variant() 
	local params="$(gen_params "${int}" "${atomic}" "$@")"

	local args="$(gen_args "$@")"



	gen_kerneldoc "raw_" "${meta}" "${pfx}" "${name}" "${sfx}" "${order}" "${atomic}" "${int}" "$@"



	printf "static __always_inline ${ret}\n"

	printf "raw_${atomicname}(${params})\n"

	printf "{\n"