From: Jeremy Kerr <jk@ozlabs.org>
Date: Thu, 4 Sep 2008 05:02:47 +0000 (+1000)
Subject: powerpc/spufs: Fix race for a free SPU
X-Git-Tag: v2.6.27-rc6~12^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b65fe0356b5b732d7e1e0224c6a1cf2eb5255984;p=pandora-kernel.git

powerpc/spufs: Fix race for a free SPU

We currently have a race for a free SPE. With one thread doing a
spu_yield(), and another doing a spu_activate():

thread 1				thread 2
spu_yield(oldctx)			spu_activate(ctx)
  __spu_deactivate(oldctx)
  spu_unschedule(oldctx, spu)
  spu->alloc_state = SPU_FREE
					spu = spu_get_idle(ctx)
					    - searches for a SPE in
					      state SPU_FREE, gets
					      the context just
					      freed by thread 1
					spu_schedule(ctx, spu)
					  spu->alloc_state = SPU_USED
spu_schedule(newctx, spu)
  - assumes spu is still free
  - tries to schedule context on
    already-used spu

This change introduces a 'free_spu' flag to spu_unschedule, to indicate
whether or not the function should free the spu after descheduling the
context. We only set this flag if we're not going to re-schedule
another context on this SPU.

Add a comment to document this behaviour.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
---

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