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From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Andrea Parri <andrea.parri@amarulasolutions.com>,
	linux-kernel@vger.kernel.org, will.deacon@arm.com,
	aou@eecs.berkeley.edu, arnd@arndb.de, bp@alien8.de,
	catalin.marinas@arm.com, davem@davemloft.net,
	fenghua.yu@intel.com, heiko.carstens@de.ibm.com,
	herbert@gondor.apana.org.au, ink@jurassic.park.msu.ru,
	jhogan@kernel.org, linux@armlinux.org.uk, mattst88@gmail.com,
	mingo@kernel.org, mpe@ellerman.id.au, palmer@sifive.com,
	paul.burton@mips.com, paulus@samba.org, ralf@linux-mips.org,
	rth@twiddle.net, stable@vger.kernel.org, tglx@linutronix.de,
	tony.luck@intel.com, vgupta@synopsys.com,
	gregkh@linuxfoundation.org, jhansen@vmware.com, vdasa@vmware.com,
	aditr@vmware.com, Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 00/18] locking/atomic: atomic64 type cleanup
Date: Fri, 24 May 2019 13:18:07 +0200
Message-ID: <20190524111807.GS2650@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190524103731.GN2606@hirez.programming.kicks-ass.net>

On Fri, May 24, 2019 at 12:37:31PM +0200, Peter Zijlstra wrote:
> On Thu, May 23, 2019 at 11:19:26AM +0100, Mark Rutland wrote:
> 
> > [mark@lakrids:~/src/linux]% git grep '\(return\|=\)\s\+atomic\(64\)\?_set'
> > include/linux/vmw_vmci_defs.h:  return atomic_set((atomic_t *)var, (u32)new_val);
> > include/linux/vmw_vmci_defs.h:  return atomic64_set(var, new_val);
> > 
> 
> Oh boy, what a load of crap you just did find.
> 
> How about something like the below? I've not read how that buffer is
> used, but the below preserves all broken without using atomic*_t.

Clarified by something along these lines?

---
 Documentation/atomic_t.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index dca3fb0554db..125c95ddbbc0 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -83,6 +83,9 @@ The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
 implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
 smp_store_release() respectively.
 
+Therefore, if you find yourself only using the Non-RMW operations of atomic_t,
+you do not in fact need atomic_t at all and are doing it wrong.
+
 The one detail to this is that atomic_set{}() should be observable to the RMW
 ops. That is:
 

  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-22 13:22 Mark Rutland
2019-05-22 13:22 ` [PATCH 01/18] locking/atomic: crypto: nx: prepare for atomic64_read() conversion Mark Rutland
2019-05-22 13:22 ` [PATCH 02/18] locking/atomic: s390/pci: " Mark Rutland
2019-05-22 13:22 ` [PATCH 03/18] locking/atomic: generic: use s64 for atomic64 Mark Rutland
2019-05-22 21:16   ` Arnd Bergmann
2019-05-22 13:22 ` [PATCH 04/18] locking/atomic: alpha: " Mark Rutland
2019-05-22 13:22 ` [PATCH 05/18] locking/atomic: arc: " Mark Rutland
2019-05-23 23:10   ` Vineet Gupta
2019-05-22 13:22 ` [PATCH 06/18] locking/atomic: arm: " Mark Rutland
2019-05-22 13:22 ` [PATCH 07/18] locking/atomic: arm64: " Mark Rutland
2019-05-22 13:22 ` [PATCH 08/18] locking/atomic: ia64: " Mark Rutland
2019-05-22 13:22 ` [PATCH 09/18] locking/atomic: mips: " Mark Rutland
2019-05-22 13:22 ` [PATCH 10/18] locking/atomic: powerpc: " Mark Rutland
2019-05-23 13:27   ` Michael Ellerman
2019-05-22 13:22 ` [PATCH 11/18] locking/atomic: riscv: fix atomic64_sub_if_positive() offset argument Mark Rutland
2019-05-22 19:06   ` Palmer Dabbelt
2019-05-22 13:22 ` [PATCH 12/18] locking/atomic: riscv: use s64 for atomic64 Mark Rutland
2019-05-22 19:06   ` Palmer Dabbelt
2019-05-23 10:23     ` Mark Rutland
2019-05-22 13:22 ` [PATCH 13/18] locking/atomic: s390: " Mark Rutland
2019-05-22 13:22 ` [PATCH 14/18] locking/atomic: sparc: " Mark Rutland
2019-05-22 13:22 ` [PATCH 15/18] locking/atomic: x86: " Mark Rutland
2019-05-22 13:22 ` [PATCH 16/18] locking/atomic: use s64 for atomic64_t on 64-bit Mark Rutland
2019-05-22 13:22 ` [PATCH 17/18] locking/atomic: crypto: nx: remove redundant casts Mark Rutland
2019-05-22 13:22 ` [PATCH 18/18] locking/atomic: s390/pci: " Mark Rutland
2019-05-22 21:18 ` [PATCH 00/18] locking/atomic: atomic64 type cleanup Arnd Bergmann
2019-05-23 10:28   ` Mark Rutland
2019-05-23  8:30 ` Andrea Parri
2019-05-23 10:19   ` Mark Rutland
2019-05-23 11:20     ` Andrea Parri
2019-05-24 10:37     ` Peter Zijlstra
2019-05-24 11:18       ` Peter Zijlstra [this message]
2019-05-24 11:38         ` Greg KH
2019-05-24 11:42         ` Will Deacon
2019-05-24 11:52           ` Peter Zijlstra
2019-05-24 22:43             ` Andrea Parri
2019-05-28 10:47               ` Peter Zijlstra
2019-05-28 11:15                 ` Andrea Parri

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