linux-kernel - Re: [PATCH 06/11] rwsem: wake queued readers when writer blocks on active read lock

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Message-ID: <AANLkTikz2=pa5csA+pqDfKc_zYihyn+C9pUb_YNS9g0L@mail.gmail.com>
Date:	Thu, 12 Aug 2010 08:57:20 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Tony Luck <tony.luck@...el.com>,
	David Howells <dhowells@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 06/11] rwsem: wake queued readers when writer blocks on
 active read lock

On Wed, Aug 11, 2010 at 10:09 PM, Michel Lespinasse <walken@...gle.com> wrote:
> On Wed, Aug 11, 2010 at 10:02 PM, Michel Lespinasse <walken@...gle.com> wrote:
>> In arch/ia64/include/asm/rwsem.h I see RWSEM_WAITING_BIAS defined as
>> -__IA64_UL_CONST(0x0000000100000000)
>>
>> This makes it a large, positive unsigned value. This is probably
>> throwing off the rwsem_atomic_update(0, sem) < RWSEM_WAITING_BIAS
>> comparison in my patch (supposed to be long versus long, but actually
>> is long versus unsigned long on ia64).
>
> FYI, I just verified that RWSEM_WAITING_BIAS is defined as signed on
> all architectures except for ia64. So, this would be consistent with
> the issue being observed only on ia64.

Good.

Tony, can you verify that just dropping the "__IA64_UL_CONST" makes
things work for you? Having a non-working rwsem makes me really
nervous, but considering the lack of reports on other architectures, I
really do hope this is just a trivial ia64 signedness difference.

                              Linus
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