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powerpc/spufs: Fix race for a free SPU

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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>
This commit is contained in:
Jeremy Kerr 2008-09-04 15:02:47 +10:00
parent 9f43e3914d
commit b65fe0356b
1 changed files with 19 additions and 4 deletions
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23
arch/powerpc/platforms/cell/spufs/sched.c
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@ -732,13 +732,28 @@ static void spu_schedule(struct spu *spu, struct spu_context *ctx)
spu_release(ctx);
}
static void spu_unschedule(struct spu *spu, struct spu_context *ctx)
/**
* spu_unschedule - remove a context from a spu, and possibly release it.
* @spu: The SPU to unschedule from
* @ctx: The context currently scheduled on the SPU
* @free_spu Whether to free the SPU for other contexts
*
* Unbinds the context @ctx from the SPU @spu. If @free_spu is non-zero, the
* SPU is made available for other contexts (ie, may be returned by
* spu_get_idle). If this is zero, the caller is expected to schedule another
* context to this spu.
*
* Should be called with ctx->state_mutex held.
*/
static void spu_unschedule(struct spu *spu, struct spu_context *ctx,
int free_spu)
{
int node = spu->node;
mutex_lock(&cbe_spu_info[node].list_mutex);
cbe_spu_info[node].nr_active--;
spu->alloc_state = SPU_FREE;
if (free_spu)
spu->alloc_state = SPU_FREE;
spu_unbind_context(spu, ctx);
ctx->stats.invol_ctx_switch++;
spu->stats.invol_ctx_switch++;
@ -838,7 +853,7 @@ static int __spu_deactivate(struct spu_context *ctx, int force, int max_prio)
if (spu) {
new = grab_runnable_context(max_prio, spu->node);
if (new || force) {
spu_unschedule(spu, ctx);
spu_unschedule(spu, ctx, new == NULL);
if (new) {
if (new->flags & SPU_CREATE_NOSCHED)
wake_up(&new->stop_wq);
@ -911,7 +926,7 @@ static noinline void spusched_tick(struct spu_context *ctx)
new = grab_runnable_context(ctx->prio + 1, spu->node);
if (new) {
spu_unschedule(spu, ctx);
spu_unschedule(spu, ctx, 0);
if (test_bit(SPU_SCHED_SPU_RUN, &ctx->sched_flags))
spu_add_to_rq(ctx);
} else {