From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, mingo@kernel.org
Subject: Re: [RFC PATCH 3/5] asm-generic/bitops/atomic.h: Rewrite using atomic_fetch_*
Date: Mon, 19 Feb 2018 15:04:34 +0100 [thread overview]
Message-ID: <20180219140434.GS25201@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180219140142.GD30394@arm.com>
On Mon, Feb 19, 2018 at 02:01:43PM +0000, Will Deacon wrote:
> > The non serializing __clear_bit() was getting "lost"
> >
> > 80543b8e: ld_s r2,[r13,0] <--- (A) Finds PG_locked is set
> > 80543b90: or r3,r2,1 <--- (B) other core unlocks right here
> > 80543b94: st_s r3,[r13,0] <--- (C) sets PG_locked (overwrites unlock)
>
> Ah, so it's problematic for the case where atomics are built using locks.
> Got it. I'll err on the side of caution here and have the asm-generic header
> (which should be bitops/lock.h not bitops/atomic.h) conditionally define
> __clear_bit_unlock as clear_bit_lock unless the architecture has provided
> its own implementation.
So I think we get it all right if we use atomic_set_release(). If the
atomics are implemented using locks, atomic_set*() should be implemented
like atomic_xchg() and avoid the above problem.
next prev parent reply other threads:[~2018-02-20 13:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-15 15:29 [RFC PATCH 0/5] Rewrite asm-generic/bitops/atomic.h and use on arm64 Will Deacon
2018-02-15 15:29 ` [RFC PATCH 1/5] arm64: fpsimd: include <linux/init.h> in fpsimd.h Will Deacon
2018-02-15 15:29 ` [RFC PATCH 2/5] asm-generic: Avoid including linux/kernel.h in asm-generic/bug.h Will Deacon
2018-02-15 15:29 ` [RFC PATCH 3/5] asm-generic/bitops/atomic.h: Rewrite using atomic_fetch_* Will Deacon
2018-02-15 17:08 ` Peter Zijlstra
2018-02-15 18:20 ` Will Deacon
2018-02-16 10:21 ` Peter Zijlstra
2018-02-19 14:01 ` Will Deacon
2018-02-19 14:04 ` Peter Zijlstra [this message]
2018-02-16 10:35 ` Peter Zijlstra
2018-02-16 14:18 ` Peter Zijlstra
2018-02-19 14:01 ` Will Deacon
2018-02-19 14:05 ` Peter Zijlstra
2018-02-15 15:29 ` [RFC PATCH 4/5] arm64: Replace our atomic bitops implementation with asm-generic Will Deacon
2018-02-15 15:29 ` [RFC PATCH 5/5] arm64: bitops: Include <asm-generic/bitops/ext2-atomic-setbit.h> Will Deacon
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