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Date: Mon, 8 Apr 2024 10:47:46 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: elver@...gle.com, akpm@...ux-foundation.org, tglx@...utronix.de,
peterz@...radead.org, dianders@...omium.org, pmladek@...e.com,
torvalds@...ux-foundation.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH RFC cmpxchg 0/8] Provide emulation for one- and two-byte
cmpxchg()
Hello!
This series provides emulation functions for one-byte cmpxchg, and uses it
for those architectures not supporting this in hardware. The emulation
is in terms of the fully ordered four-byte cmpxchg() that is supplied
by all of these architectures. This was tested by making x86 forget
that it can do one-byte cmpxchg() natively:
88a9b3f7a924 ("EXP arch/x86: Test one-byte cmpxchg emulation")
This commit is local to -rcu and is of course not intended for mainline.
If accepted, RCU Tasks will use this capability in place of the current
rcu_trc_cmpxchg_need_qs() open-coding of this emulation.
1. sparc32: make __cmpxchg_u32() return u32, courtesy of Al Viro.
2. sparc32: make the first argument of __cmpxchg_u64() volatile u64 *,
courtesy of Al Viro.
3. sparc32: unify __cmpxchg_u{32,64}, courtesy of Al Viro.
4. sparc32: add __cmpxchg_u{8,16}() and teach __cmpxchg() to handle those
sizes, courtesy of Al Viro.
5. parisc: __cmpxchg_u32(): lift conversion into the callers, courtesy of
Al Viro.
6. parisc: unify implementations of __cmpxchg_u{8,32,64}, courtesy of
Al Viro.
7. parisc: add missing export of __cmpxchg_u8(), courtesy of Al Viro.
8. parisc: add u16 support to cmpxchg(), courtesy of Al Viro.
9. lib: Add one-byte emulation function.
10. ARC: Emulate one-byte cmpxchg.
11. csky: Emulate one-byte cmpxchg.
12. sh: Emulate one-byte cmpxchg.
13. xtensa: Emulate one-byte cmpxchg.
14. riscv: Emulate one-byte cmpxchg.
Changes since v1:
o Add native support for sparc32 and parisc, courtesy of Al Viro.
o Remove two-byte emulation due to architectures that still do not
support two-byte load and store instructions, per Arnd Bergmann
feedback. (Yes, there are a few systems out there that do not
even support one-byte load instructions, but these are slated
for removal anyway.)
o Fix numerous casting bugs spotted by kernel test robot.
o Fix SPDX header. "//" for .c files and "/*" for .h files.
I am sure that there is a good reason for this. ;-)
Thanx, Paul
------------------------------------------------------------------------
arch/parisc/include/asm/cmpxchg.h | 19 +++++-------
arch/parisc/kernel/parisc_ksyms.c | 1
arch/parisc/lib/bitops.c | 52 +++++++++++-----------------------
arch/sparc/include/asm/cmpxchg_32.h | 18 +++++------
arch/sparc/lib/atomic32.c | 47 +++++++++++++-----------------
b/arch/Kconfig | 3 +
b/arch/arc/Kconfig | 1
b/arch/arc/include/asm/cmpxchg.h | 32 +++++++++++++++-----
b/arch/csky/Kconfig | 1
b/arch/csky/include/asm/cmpxchg.h | 10 ++++++
b/arch/parisc/include/asm/cmpxchg.h | 3 -
b/arch/parisc/kernel/parisc_ksyms.c | 1
b/arch/parisc/lib/bitops.c | 6 +--
b/arch/riscv/Kconfig | 1
b/arch/riscv/include/asm/cmpxchg.h | 13 ++++++++
b/arch/sh/Kconfig | 1
b/arch/sh/include/asm/cmpxchg.h | 2 +
b/arch/sparc/include/asm/cmpxchg_32.h | 4 +-
b/arch/sparc/lib/atomic32.c | 4 +-
b/arch/xtensa/Kconfig | 1
b/arch/xtensa/include/asm/cmpxchg.h | 2 +
b/include/linux/cmpxchg-emu.h | 15 +++++++++
b/lib/Makefile | 1
b/lib/cmpxchg-emu.c | 45 +++++++++++++++++++++++++++++
24 files changed, 184 insertions(+), 99 deletions(-)
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