[PATCH 7/8] powerpc/pseries: Protect against hogging the cpu while setting up the stats

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

When enabling or disabling the vcpu dispatch statistics, we do a lot of
work including allocating/deallocating memory across all possible cpus
for the DTL buffer. In order to guard against hogging the cpu for too
long, track the time we're taking and yield the processor if necessary.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/plpar_wrappers.h |  2 +-
 arch/powerpc/platforms/pseries/lpar.c     | 29 ++++++++++++++++-------
 arch/powerpc/platforms/pseries/setup.c    |  2 +-
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/include/asm/plpar_wrappers.h b/arch/powerpc/include/asm/plpar_wrappers.h
index ab7dd454b6eb..d01bf0036e4d 100644
--- a/arch/powerpc/include/asm/plpar_wrappers.h
+++ b/arch/powerpc/include/asm/plpar_wrappers.h
@@ -91,7 +91,7 @@ static inline long register_dtl(unsigned long cpu, unsigned long vpa)
 extern bool register_dtl_buffer_access(bool global);
 extern void unregister_dtl_buffer_access(bool global);
 extern void register_dtl_buffer(int cpu);
-extern void alloc_dtl_buffers(void);
+extern void alloc_dtl_buffers(unsigned long *time_limit);
 extern void vpa_init(int cpu);
 
 static inline long plpar_pte_enter(unsigned long flags,
diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index b808a70cc253..8bc1b950cfd0 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -257,7 +257,7 @@ static void process_dtl_buffer(struct work_struct *work)
 					HZ / vcpudispatch_stats_freq);
 }
 
-void alloc_dtl_buffers(void)
+void alloc_dtl_buffers(unsigned long *time_limit)
 {
 	int cpu;
 	struct paca_struct *pp;
@@ -281,10 +281,15 @@ void alloc_dtl_buffers(void)
 		pp->dispatch_log = dtl;
 		pp->dispatch_log_end = dtl + N_DISPATCH_LOG;
 		pp->dtl_curr = dtl;
+
+		if (time_limit && time_after(jiffies, *time_limit)) {
+			cond_resched();
+			*time_limit = jiffies + HZ;
+		}
 	}
 }
 
-static void free_dtl_buffers(void)
+static void free_dtl_buffers(unsigned long *time_limit)
 {
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 	int cpu;
@@ -299,6 +304,11 @@ static void free_dtl_buffers(void)
 		pp->dispatch_log = 0;
 		pp->dispatch_log_end = 0;
 		pp->dtl_curr = 0;
+
+		if (time_limit && time_after(jiffies, *time_limit)) {
+			cond_resched();
+			*time_limit = jiffies + HZ;
+		}
 	}
 #endif
 }
@@ -381,7 +391,7 @@ static void reset_global_dtl_mask(void)
 		lppaca_of(cpu).dtl_enable_mask = dtl_mask;
 }
 
-static int dtl_worker_enable(void)
+static int dtl_worker_enable(unsigned long *time_limit)
 {
 	int rc = 0, state;
 
@@ -400,13 +410,13 @@ static int dtl_worker_enable(void)
 	set_global_dtl_mask(DTL_LOG_ALL);
 
 	/* Setup dtl buffers and register those */
-	alloc_dtl_buffers();
+	alloc_dtl_buffers(time_limit);
 
 	state = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "powerpc/dtl:online",
 					dtl_worker_online, dtl_worker_offline);
 	if (state < 0) {
 		pr_err("vcpudispatch_stats: unable to setup workqueue for DTL processing\n");
-		free_dtl_buffers();
+		free_dtl_buffers(time_limit);
 		reset_global_dtl_mask();
 		unregister_dtl_buffer_access(1);
 		rc = -EINVAL;
@@ -420,14 +430,14 @@ static int dtl_worker_enable(void)
 	return rc;
 }
 
-static void dtl_worker_disable(void)
+static void dtl_worker_disable(unsigned long *time_limit)
 {
 	mutex_lock(&dtl_worker_mutex);
 	dtl_worker_refctr--;
 	if (!dtl_worker_refctr) {
 		cpuhp_remove_state(dtl_worker_state);
 		dtl_worker_state = 0;
-		free_dtl_buffers();
+		free_dtl_buffers(time_limit);
 		reset_global_dtl_mask();
 		unregister_dtl_buffer_access(1);
 	}
@@ -437,6 +447,7 @@ static void dtl_worker_disable(void)
 static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
 		size_t count, loff_t *ppos)
 {
+	unsigned long time_limit = jiffies + HZ;
 	struct vcpu_dispatch_data *disp;
 	int rc, cmd, cpu;
 	char buf[16];
@@ -469,13 +480,13 @@ static ssize_t vcpudispatch_stats_write(struct file *file, const char __user *p,
 			disp->last_disp_cpu = -1;
 		}
 
-		rc = dtl_worker_enable();
+		rc = dtl_worker_enable(&time_limit);
 		if (rc) {
 			destroy_cpu_associativity();
 			return rc;
 		}
 	} else {
-		dtl_worker_disable();
+		dtl_worker_disable(&time_limit);
 		destroy_cpu_associativity();
 	}
 
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index b6995e5cc5c9..c98246343752 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -283,7 +283,7 @@ static int alloc_dispatch_logs(void)
 	if (!dtl_cache)
 		return 0;
 
-	alloc_dtl_buffers();
+	alloc_dtl_buffers(0);
 
 	/* Register the DTL for the current (boot) cpu */
 	register_dtl_buffer(smp_processor_id());
-- 
2.21.0