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Date: Wed, 6 Jan 2016 13:19:44 +0200 From: "Michael S. Tsirkin" <mst@...hat.com> To: Rich Felker <dalias@...c.org> Cc: linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org, peterz@...radead.org Subject: Re: [PATCH v2 31/32] sh: support a 2-byte smp_store_mb On Tue, Jan 05, 2016 at 06:27:35PM -0500, Rich Felker wrote: > On Thu, Dec 31, 2015 at 09:09:47PM +0200, Michael S. Tsirkin wrote: > > At the moment, xchg on sh only supports 4 and 1 byte values, so using it > > from smp_store_mb means attempts to store a 2 byte value using this > > macro fail. > > > > And happens to be exactly what virtio drivers want to do. > > > > Check size and fall back to a slower, but safe, WRITE_ONCE+smp_mb. > > Can you please do this for size 1 as well (i.e. all sizes != 4)? If > you check the source, the code for size-1 xchg in sh cmpxchg-llsc.h is > completely wrong and operates on a 32-bit object at the address passed > to it. This code is presently unused anyway and I plan to submit a > patch to remove the size 1 case. > > Rich Ouch. And PeterZ says I should write a 2-byte xchg in asm instead, and Fedora can't even build a full kernel for this arch at the moment :( Peter, what do you think? How about I leave this patch as is for now? -- MST -- 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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