linux-kernel - Re: [PATCH] RISC-V: Break load reservations during switch

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Message-ID: <87ftom4ij2.fsf@igel.home>
Date:   Thu, 06 Jun 2019 21:32:01 +0200
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>, marco@...red.org,
        me@...losedp.com, joel@...g.id.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RISC-V: Break load reservations during switch_to

On Jun 06 2019, Christoph Hellwig <hch@...radead.org> wrote:

> On Wed, Jun 05, 2019 at 04:17:35PM -0700, Palmer Dabbelt wrote:
>>  	REG_S ra,  TASK_THREAD_RA_RA(a3)
>> +	/*
>> +	 * The Linux ABI allows programs to depend on load reservations being
>> +	 * broken on context switches, but the ISA doesn't require that the
>> +	 * hardware ever breaks a load reservation.  The only way to break a
>> +	 * load reservation is with a store conditional, so we emit one here.
>> +	 * Since nothing ever takes a load reservation on TASK_THREAD_RA_RA we
>> +	 * know this will always fail, but just to be on the safe side this
>> +	 * writes the same value that was unconditionally written by the
>> +	 * previous instruction.
>> +	 */
>> +#if (TASK_THREAD_RA_RA != 0)
>
> I don't think this check works as intended.  TASK_THREAD_RA_RA is a
> parameterized macro,

Is it?  Just because it is used before an open paren doesn't mean that
the macro takes a parameter.

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
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