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>
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 9bb45c6..897c740 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -732,13 +732,28 @@
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 @@
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 @@
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 {
