Messages in this thread | | | Date | Mon, 6 May 2013 21:26:28 +0100 | From | Al Viro <> | Subject | Re: [PATCH] alpha: spinlock: don't perform memory access in locked critical section |
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On Mon, May 06, 2013 at 09:01:05PM +0100, Will Deacon wrote: > The Alpha Architecture Reference Manual states that any memory access > performed between an LD_xL and a STx_C instruction may cause the > store-conditional to fail unconditionally and, as such, `no useful > program should do this'. > > Linux is a useful program, so fix up the Alpha spinlock implementation > to use logical operations rather than load-address instructions for > generating immediates.
Huh? Relevant quote is "If any other memory access (ECB, LDx, LDQ_U, STx_C, STQ_U, WH64x) is executed on the given processor between the LDx_L and the STx_C, the sequence above may always fail on some implementations; hence, no no useful programs should do this". Where do you see LDA in that list and why would it possibly be there? And no, LDx does *not* cover it - the same reference manual gives LD{Q,L,WU,BU} as expansion for LDx, using LDAx for LD{A,AH}; it's a separate group of instructions and it does *NOT* do any kind of memory access.
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