From: Russell King <rmk+lkml@arm.linux.org.uk>
To: David Howells <dhowells@redhat.com>
Cc: Andrew Morton <akpm@osdl.org>,
torvalds@osdl.org, davem@davemloft.com, wli@holomorphy.com,
matthew@wil.cx, linux-kernel@vger.kernel.org,
linux-arch@vger.kernel.org
Subject: Re: [PATCH 3/3] WorkStruct: Use direct assignment rather than cmpxchg()
Date: Thu, 7 Dec 2006 23:42:51 +0000 [thread overview]
Message-ID: <20061207234250.GH1255@flint.arm.linux.org.uk> (raw)
In-Reply-To: <639.1165521999@redhat.com>
On Thu, Dec 07, 2006 at 08:06:39PM +0000, David Howells wrote:
> Andrew Morton <akpm@osdl.org> wrote:
>
> > and we can assume (and ensure) that a failing test_and_set_bit() will not
> > write to the affected word at all.
>
> You may not assume that; and indeed that is not so in the generic
> spinlock-based bitops or ARM pre-v6 or PA-RISC or sparc32 or ...
Incorrect. pre-v6 ARM bitops for test_and_xxx_bit() all do:
save and disable irqs
load value
test bit
if not in desired state, alter bit and write it back
restore irqs
but I don't guarantee that we'll always do that - indeed, post-armv6
bitops always write back even if the bit was in the desired state.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
next prev parent reply other threads:[~2006-12-07 23:43 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-07 15:31 [PATCH 1/3] WorkStruct: Fix up some PA-RISC work items David Howells
2006-12-07 15:31 ` [PATCH 2/3] WorkStruct: Add assign_bits() to give an atomic-bitops safe assignment David Howells
2006-12-07 15:31 ` [PATCH 3/3] WorkStruct: Use direct assignment rather than cmpxchg() David Howells
2006-12-07 16:54 ` Andrew Morton
2006-12-07 20:06 ` David Howells
2006-12-07 21:06 ` Andrew Morton
2006-12-07 21:06 ` James Bottomley
2006-12-07 21:16 ` David Howells
2006-12-07 22:11 ` David Miller
2006-12-07 23:42 ` Russell King [this message]
2006-12-07 23:58 ` David Howells
2006-12-08 11:14 ` Russell King
2006-12-08 13:57 ` David Howells
2006-12-08 3:42 ` [PATCH 1/3] WorkStruct: Fix up some PA-RISC work items Kyle McMartin
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