workqueue: reimplement workqueue freeze using max_active

Currently, workqueue freezing is implemented by marking the worker
freezeable and calling try_to_freeze() from dispatch loop.
Reimplement it using cwq->limit so that the workqueue is frozen
instead of the worker.

* workqueue_struct->saved_max_active is added which stores the
  specified max_active on initialization.

* On freeze, all cwq->max_active's are quenched to zero.  Freezing is
  complete when nr_active on all cwqs reach zero.

* On thaw, all cwq->max_active's are restored to wq->saved_max_active
  and the worklist is repopulated.

This new implementation allows having single shared pool of workers
per cpu.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 19 insertions, 2 deletions

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 71ae290..028a995 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -15,6 +15,7 @@
 #include <linux/syscalls.h>
 #include <linux/freezer.h>
 #include <linux/delay.h>
+#include <linux/workqueue.h>
 
 /* 
  * Timeout for stopping processes
@@ -35,6 +36,7 @@ static int try_to_freeze_tasks(bool sig_only)
 	struct task_struct *g, *p;
 	unsigned long end_time;
 	unsigned int todo;
+	bool wq_busy = false;
 	struct timeval start, end;
 	u64 elapsed_csecs64;
 	unsigned int elapsed_csecs;
@@ -42,6 +44,10 @@ static int try_to_freeze_tasks(bool sig_only)
 	do_gettimeofday(&start);
 
 	end_time = jiffies + TIMEOUT;
+
+	if (!sig_only)
+		freeze_workqueues_begin();
+
 	while (true) {
 		todo = 0;
 		read_lock(&tasklist_lock);
@@ -63,6 +69,12 @@ static int try_to_freeze_tasks(bool sig_only)
 				todo++;
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
+
+		if (!sig_only) {
+			wq_busy = freeze_workqueues_busy();
+			todo += wq_busy;
+		}
+
 		if (!todo || time_after(jiffies, end_time))
 			break;
 
@@ -86,8 +98,12 @@ static int try_to_freeze_tasks(bool sig_only)
 		 */
 		printk("\n");
 		printk(KERN_ERR "Freezing of tasks failed after %d.%02d seconds "
-				"(%d tasks refusing to freeze):\n",
-				elapsed_csecs / 100, elapsed_csecs % 100, todo);
+		       "(%d tasks refusing to freeze, wq_busy=%d):\n",
+		       elapsed_csecs / 100, elapsed_csecs % 100,
+		       todo - wq_busy, wq_busy);
+
+		thaw_workqueues();
+
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
 			task_lock(p);
@@ -157,6 +173,7 @@ void thaw_processes(void)
 	oom_killer_enable();
 
 	printk("Restarting tasks ... ");
+	thaw_workqueues();
 	thaw_tasks(true);
 	thaw_tasks(false);
 	schedule();