Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b65fe035 authored by Jeremy Kerr's avatar Jeremy Kerr
Browse files

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: default avatarJeremy Kerr <jk@ozlabs.org>
parent 9f43e391

arch/powerpc/platforms/cell/spufs/sched.c

+19 −4
Original line number Diff line number Diff line
@@ -732,12 +732,27 @@ 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--;

	if (free_spu)

		spu->alloc_state = SPU_FREE;

	spu_unbind_context(spu, ctx);

	ctx->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 {