From patchwork series 481783

https://patchwork.ozlabs.org//project/linuxppc-dev/list/?series=481783

Author: Fox Snowpatch

arch/powerpc/include/asm/dtl.h

@@ -40,4 +40,5 @@ extern struct rw_semaphore dtl_access_lock;
 extern void register_dtl_buffer(int cpu);
 extern void alloc_dtl_buffers(unsigned long *time_limit);
 
+extern atomic_t dtl_count;
 #endif /* _ASM_POWERPC_DTL_H */

arch/powerpc/platforms/pseries/dtl.c

@@ -37,6 +37,14 @@ static u8 dtl_event_mask = DTL_LOG_ALL;
  */
 static int dtl_buf_entries = N_DISPATCH_LOG;
 
+/*
+ * dtl_count indicates the number and type of dtl users.
+ *  0 indicates no active users of dtl / vcpu_dispatchstats.
+ * -1 indicates vcpudispatch_stats user is active.
+ * 1 and above indicates active dtl users.
+ */
+atomic_t dtl_count;
+
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 
 /*
@@ -56,8 +64,6 @@ struct dtl_ring {
 
 static DEFINE_PER_CPU(struct dtl_ring, dtl_rings);
 
-static atomic_t dtl_count;
-
 /*
  * The cpu accounting code controls the DTL ring buffer, and we get
  * given entries as they are processed.
@@ -158,7 +164,7 @@ static int dtl_start(struct dtl *dtl)
 
 	/* enable event logging */
 	lppaca_of(dtl->cpu).dtl_enable_mask = dtl_event_mask;
-
+	atomic_inc(&dtl_count);
 	return 0;
 }
 
@@ -169,6 +175,7 @@ static void dtl_stop(struct dtl *dtl)
 	lppaca_of(dtl->cpu).dtl_enable_mask = 0x0;
 
 	unregister_dtl(hwcpu);
+	atomic_dec(&dtl_count);
 }
 
 static u64 dtl_current_index(struct dtl *dtl)
@@ -194,6 +201,11 @@ static int dtl_enable(struct dtl *dtl)
 	if (!down_read_trylock(&dtl_access_lock))
 		return -EBUSY;
 
+	if (atomic_read(&dtl_count) == -1) {
+		up_read(&dtl_access_lock);
+		return -EBUSY;
+	}
+
 	n_entries = dtl_buf_entries;
 	buf = kmem_cache_alloc_node(dtl_cache, GFP_KERNEL, cpu_to_node(dtl->cpu));
 	if (!buf) {

arch/powerpc/platforms/pseries/lpar.c

@@ -175,7 +175,6 @@ static DEFINE_PER_CPU(struct vcpu_dispatch_data, vcpu_disp_data);
 static DEFINE_PER_CPU(u64, dtl_entry_ridx);
 static DEFINE_PER_CPU(struct dtl_worker, dtl_workers);
 static enum cpuhp_state dtl_worker_state;
-static DEFINE_MUTEX(dtl_enable_mutex);
 static int vcpudispatch_stats_on __read_mostly;
 static int vcpudispatch_stats_freq = 50;
 static __be32 *vcpu_associativity, *pcpu_associativity;
@@ -464,7 +463,8 @@ static int dtl_worker_enable(unsigned long *time_limit)
 {
 	int rc = 0, state;
 
-	if (!down_write_trylock(&dtl_access_lock)) {
+	/* Return if dtl is already active */
+	if (atomic_read(&dtl_count) != 0) {
 		rc = -EBUSY;
 		goto out;
 	}
@@ -480,11 +480,11 @@ static int dtl_worker_enable(unsigned long *time_limit)
 		pr_err("vcpudispatch_stats: unable to setup workqueue for DTL processing\n");
 		free_dtl_buffers(time_limit);
 		reset_global_dtl_mask();
-		up_write(&dtl_access_lock);
 		rc = -EINVAL;
 		goto out;
 	}
 	dtl_worker_state = state;
+	atomic_set(&dtl_count, -1);
 
 out:
 	return rc;
@@ -495,7 +495,7 @@ static void dtl_worker_disable(unsigned long *time_limit)
 	cpuhp_remove_state(dtl_worker_state);
 	free_dtl_buffers(time_limit);
 	reset_global_dtl_mask();
-	up_write(&dtl_access_lock);
+	atomic_set(&dtl_count, 0);
 }
 
 static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
@@ -519,7 +519,8 @@ static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
 		return rc ? rc : -EINVAL;
 	}
 
-	mutex_lock(&dtl_enable_mutex);
+	if (!down_write_trylock(&dtl_access_lock))
+		return -EBUSY;
 
 	if ((cmd == 0 && !vcpudispatch_stats_on) ||
 			(cmd == 1 && vcpudispatch_stats_on))
@@ -551,7 +552,7 @@ static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
 	vcpudispatch_stats_on = cmd;
 
 out:
-	mutex_unlock(&dtl_enable_mutex);
+	up_write(&dtl_access_lock);
 	if (rc)
 		return rc;
 	return count;