[POWERPC] spufs: Fix race condition on gang->aff_ref_spu

Affinity reference point location (gang->aff_ref_spu) is reset
when the whole gang is descheduled. However, the last member of
a gang can be descheduled while we are trying to schedule another
member of the gang. This was leading to a race condition, and
the code was using gang->aff_ref_spu in an unsafe manner.

By holding the gang->aff_mutex a little bit longer, and increment
gang->aff_sched_count (which controls when gang->aff_ref_spu
should be reset) a little bit earlier, the problem is fixed.

Signed-off-by: Andre Detsch <adetsch@br.ibm.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 32 insertions, 17 deletions

diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index c784edd40ea7..17806e001e50 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -230,8 +230,6 @@ static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
 
         if (ctx->flags & SPU_CREATE_NOSCHED)
                 atomic_inc(&cbe_spu_info[spu->node].reserved_spus);
-        if (!list_empty(&ctx->aff_list))
-                atomic_inc(&ctx->gang->aff_sched_count);
 
         ctx->stats.slb_flt_base = spu->stats.slb_flt;
         ctx->stats.class2_intr_base = spu->stats.class2_intr;
@@ -392,7 +390,6 @@ static int has_affinity(struct spu_context *ctx)
         if (list_empty(&ctx->aff_list))
                 return 0;
 
-        mutex_lock(&gang->aff_mutex);
         if (!gang->aff_ref_spu) {
                 if (!(gang->aff_flags & AFF_MERGED))
                         aff_merge_remaining_ctxs(gang);
@@ -400,7 +397,6 @@ static int has_affinity(struct spu_context *ctx)
                         aff_set_offsets(gang);
                 aff_set_ref_point_location(gang);
         }
-        mutex_unlock(&gang->aff_mutex);
 
         return gang->aff_ref_spu != NULL;
 }
@@ -418,9 +414,16 @@ static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
 
         if (spu->ctx->flags & SPU_CREATE_NOSCHED)
                 atomic_dec(&cbe_spu_info[spu->node].reserved_spus);
-        if (!list_empty(&ctx->aff_list))
-                if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
-                        ctx->gang->aff_ref_spu = NULL;
+
+        if (ctx->gang){
+                mutex_lock(&ctx->gang->aff_mutex);
+                if (has_affinity(ctx)) {
+                        if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
+                                ctx->gang->aff_ref_spu = NULL;
+                }
+                mutex_unlock(&ctx->gang->aff_mutex);
+        }
+
         spu_switch_notify(spu, NULL);
         spu_unmap_mappings(ctx);
         spu_save(&ctx->csa, spu);
@@ -511,20 +514,32 @@ static void spu_prio_wait(struct spu_context *ctx)
 
 static struct spu *spu_get_idle(struct spu_context *ctx)
 {
-        struct spu *spu;
+        struct spu *spu, *aff_ref_spu;
         int node, n;
 
-        if (has_affinity(ctx)) {
-                node = ctx->gang->aff_ref_spu->node;
+        if (ctx->gang) {
+                mutex_lock(&ctx->gang->aff_mutex);
+                if (has_affinity(ctx)) {
+                        aff_ref_spu = ctx->gang->aff_ref_spu;
+                        atomic_inc(&ctx->gang->aff_sched_count);
+                        mutex_unlock(&ctx->gang->aff_mutex);
+                        node = aff_ref_spu->node;
 
-                mutex_lock(&cbe_spu_info[node].list_mutex);
-                spu = ctx_location(ctx->gang->aff_ref_spu, ctx->aff_offset, node);
-                if (spu && spu->alloc_state == SPU_FREE)
-                        goto found;
-                mutex_unlock(&cbe_spu_info[node].list_mutex);
-                return NULL;
-        }
+                        mutex_lock(&cbe_spu_info[node].list_mutex);
+                        spu = ctx_location(aff_ref_spu, ctx->aff_offset, node);
+                        if (spu && spu->alloc_state == SPU_FREE)
+                                goto found;
+                        mutex_unlock(&cbe_spu_info[node].list_mutex);
 
+                        mutex_lock(&ctx->gang->aff_mutex);
+                        if (atomic_dec_and_test(&ctx->gang->aff_sched_count))
+                                ctx->gang->aff_ref_spu = NULL;
+                        mutex_unlock(&ctx->gang->aff_mutex);
+
+                        return NULL;
+                }
+                mutex_unlock(&ctx->gang->aff_mutex);
+        }
         node = cpu_to_node(raw_smp_processor_id());
         for (n = 0; n < MAX_NUMNODES; n++, node++) {
                 node = (node < MAX_NUMNODES) ? node : 0;