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Date: Wed, 27 May 2009 20:08:27 +0200 From: Andi Kleen <andi@...stfloor.org> To: Harald Welte <HaraldWelte@...tech.com> Cc: "H. Peter Anvin" <hpa@...or.com>, lkml@...ethan.org, Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: LOCK prefix on uni processor has its use Harald Welte <HaraldWelte@...tech.com> writes: > * All X86 instructions except rep-strings are atomic wrt interrupts. > * The lock prefix has uses on a UP processor: It keeps DMA devices from > interfering with a read-modify-write sequence In theory yes, but not in Linux -- normal drivers simply don't use LOCK in any way on a UP kernel. We discussed exactly this in the earlier subthread :) > Now the question is: Is this a valid operation of a driver? Should the driver > do such things, or is such a driver broken? The driver is broken because if it relies on this it will not work on a UP kernel. Also it's not portable and in general a bad idea. > When would that occur? I'm trying > to come up with a case, but typically you e.g. allocate some DMA buffer and > then don't touch it until the hardware has processed it. Is it known which driver has this problem? -Andi (who finds hpa's "timing theory" to be more believable anyways) -- ak@...ux.intel.com -- Speaking for myself only. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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