linux-kernel - [PATCH 4/9] tools: Take @bit as an "unsigned long" in {clear,set}

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Message-ID: <20221119013450.2643007-5-seanjc@google.com>
Date:   Sat, 19 Nov 2022 01:34:45 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yury Norov <yury.norov@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH 4/9] tools: Take @bit as an "unsigned long" in
 {clear,set}_bit() helpers

Take @bit as an unsigned long instead of a signed int in clear_bit() and
set_bit() so that they match the double-underscore versions, __clear_bit()
and __set_bit().  This will allow converting users that really don't want
atomic operations to the double-underscores without introducing a
functional change, which will in turn allow making {clear,set}_bit()
atomic (as advertised).

Practically speaking, this _should_ have no functional impact.  KVM's
selftests usage is either hardcoded (Hyper-V tests) or is artificially
limited (arch_timer test and dirty_log test).  In KVM, dirty_log test is
the only mildly interesting case as it's use indirectly restricted to
unsigned 32-bit values, but in theory it could generate a negative value
when cast to a signed int.  But in that case, taking an "unsigned long"
is actually a bug fix.

Perf's usage is more difficult to audit, but any code that is affected
by the switch is likely already broken.  perf_header__{set,clear}_feat()
and perf_file_header__read() effectively use only hardcoded enums with
small, positive values, atom_new() passes an unsigned long, but its value
is capped at 128 via NR_ATOM_PER_PAGE, etc...

The only real potential for breakage is in the perf flows that take a
"cpu", but it's unlikely perf is subtly relying on a negative index into
bitmaps, e.g. "cpu" can be "-1", but only as "not valid" placeholder.

Note, tools/testing/nvdimm/ makes heavy use of set_bit(), but that code
builds into a kernel module of sorts, i.e. pulls in all of the kernel's
header and so is getting the kernel's atomic set_bit().  The NVDIMM test
usage of atomics is likely unnecessary, e.g. ndtest_dimm_register() sets
bits in a local variable, but that's neither here nor there as far as
this change is concerned.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 tools/include/asm-generic/bitops/atomic.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/include/asm-generic/bitops/atomic.h b/tools/include/asm-generic/bitops/atomic.h
index 2f6ea28764a7..f64b049d236c 100644
--- a/tools/include/asm-generic/bitops/atomic.h
+++ b/tools/include/asm-generic/bitops/atomic.h
@@ -5,12 +5,12 @@
 #include <asm/types.h>
 #include <asm/bitsperlong.h>

-static inline void set_bit(int nr, unsigned long *addr)
+static inline void set_bit(unsigned long nr, unsigned long *addr)
 {
 	addr[nr / __BITS_PER_LONG] |= 1UL << (nr % __BITS_PER_LONG);
 }

-static inline void clear_bit(int nr, unsigned long *addr)
+static inline void clear_bit(unsigned long nr, unsigned long *addr)
 {
 	addr[nr / __BITS_PER_LONG] &= ~(1UL << (nr % __BITS_PER_LONG));
 }
-- 
2.38.1.584.g0f3c55d4c2-goog