relay: use plain timer instead of delayed work

relay doesn't need to use schedule_delayed_work() for waking readers
when a simple timer will do.

Signed-off-by: Tom Zanussi <zanussi@comcast.net>
Cc: Satyam Sharma <satyam.sharma@gmail.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 18 insertions, 20 deletions

diff --git a/include/linux/relay.h b/include/linux/relay.h
index 759a0f97bec2..6cd8c4425fc7 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -12,6 +12,7 @@
 
 #include <linux/types.h>
 #include <linux/sched.h>
+#include <linux/timer.h>
 #include <linux/wait.h>
 #include <linux/list.h>
 #include <linux/fs.h>
@@ -38,7 +39,7 @@ struct rchan_buf
         size_t subbufs_consumed;        /* count of sub-buffers consumed */
         struct rchan *chan;             /* associated channel */
         wait_queue_head_t read_wait;    /* reader wait queue */
-        struct delayed_work wake_readers; /* reader wake-up work struct */
+        struct timer_list timer;        /* reader wake-up timer */
         struct dentry *dentry;          /* channel file dentry */
         struct kref kref;               /* channel buffer refcount */
         struct page **page_array;       /* array of current buffer pages */
diff --git a/kernel/relay.c b/kernel/relay.c
index 577f251c7e28..e804589c863c 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -310,16 +310,13 @@ static struct rchan_callbacks default_channel_callbacks = {
 
 /**
  *      wakeup_readers - wake up readers waiting on a channel
- *      @work: work struct that contains the the channel buffer
+ *      @data: contains the the channel buffer
  *
- *      This is the work function used to defer reader waking.  The
- *      reason waking is deferred is that calling directly from write
- *      causes problems if you're writing from say the scheduler.
+ *      This is the timer function used to defer reader waking.
  */
-static void wakeup_readers(struct work_struct *work)
+static void wakeup_readers(unsigned long data)
 {
-        struct rchan_buf *buf =
-                container_of(work, struct rchan_buf, wake_readers.work);
+        struct rchan_buf *buf = (struct rchan_buf *)data;
         wake_up_interruptible(&buf->read_wait);
 }
 
@@ -337,11 +334,9 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
         if (init) {
                 init_waitqueue_head(&buf->read_wait);
                 kref_init(&buf->kref);
-                INIT_DELAYED_WORK(&buf->wake_readers, NULL);
-        } else {
-                cancel_delayed_work(&buf->wake_readers);
-                flush_scheduled_work();
-        }
+                setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
+        } else
+                del_timer_sync(&buf->timer);
 
         buf->subbufs_produced = 0;
         buf->subbufs_consumed = 0;
@@ -447,8 +442,7 @@ end:
 static void relay_close_buf(struct rchan_buf *buf)
 {
         buf->finalized = 1;
-        cancel_delayed_work(&buf->wake_readers);
-        flush_scheduled_work();
+        del_timer_sync(&buf->timer);
         kref_put(&buf->kref, relay_remove_buf);
 }
 
@@ -608,11 +602,14 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
                 buf->dentry->d_inode->i_size += buf->chan->subbuf_size -
                         buf->padding[old_subbuf];
                 smp_mb();
-                if (waitqueue_active(&buf->read_wait)) {
-                        PREPARE_DELAYED_WORK(&buf->wake_readers,
-                                             wakeup_readers);
-                        schedule_delayed_work(&buf->wake_readers, 1);
-                }
+                if (waitqueue_active(&buf->read_wait))
+                        /*
+                         * Calling wake_up_interruptible() from here
+                         * will deadlock if we happen to be logging
+                         * from the scheduler (trying to re-grab
+                         * rq->lock), so defer it.
+                         */
+                        __mod_timer(&buf->timer, jiffies + 1);
         }
 
         old = buf->data;