ext4: Use schedule_timeout_interruptible() for waiting in lazyinit thread

In order to make lazyinit eat approx. 10% of io bandwidth at max, we
are sleeping between zeroing each single inode table. For that purpose
we are using timer which wakes up thread when it expires. It is set
via add_timer() and this may cause troubles in the case that thread
has been woken up earlier and in next iteration we call add_timer() on
still running timer hence hitting BUG_ON in add_timer(). We could fix
that by using mod_timer() instead however we can use
schedule_timeout_interruptible() for waiting and hence simplifying
things a lot.

This commit exchange the old "waiting mechanism" with simple
schedule_timeout_interruptible(), setting the time to sleep. Hence we
do not longer need li_wait_daemon waiting queue and others, so get rid
of it.

Addresses-Red-Hat-Bugzilla: #699708

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>

2 files changed, 6 insertions, 29 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 47986ae8dcec..579dfeda614c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1605,12 +1605,8 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr,
  */
 struct ext4_lazy_init {
         unsigned long           li_state;
-
-        wait_queue_head_t       li_wait_daemon;
         wait_queue_head_t       li_wait_task;
-        struct timer_list       li_timer;
         struct task_struct      *li_task;
-
         struct list_head        li_request_list;
         struct mutex            li_list_mtx;
 };
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a1f12bab9425..6a40ec1aabf6 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2673,12 +2673,6 @@ static void print_daily_error_info(unsigned long arg)
         mod_timer(&sbi->s_err_report, jiffies + 24*60*60*HZ);  /* Once a day */
 }
 
-static void ext4_lazyinode_timeout(unsigned long data)
-{
-        struct task_struct *p = (struct task_struct *)data;
-        wake_up_process(p);
-}
-
 /* Find next suitable group and run ext4_init_inode_table */
 static int ext4_run_li_request(struct ext4_li_request *elr)
 {
@@ -2726,7 +2720,7 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
 
 /*
  * Remove lr_request from the list_request and free the
- * request tructure. Should be called with li_list_mtx held
+ * request structure. Should be called with li_list_mtx held
  */
 static void ext4_remove_li_request(struct ext4_li_request *elr)
 {
@@ -2770,14 +2764,10 @@ static int ext4_lazyinit_thread(void *arg)
         struct ext4_lazy_init *eli = (struct ext4_lazy_init *)arg;
         struct list_head *pos, *n;
         struct ext4_li_request *elr;
-        unsigned long next_wakeup;
-        DEFINE_WAIT(wait);
+        unsigned long next_wakeup, cur;
 
         BUG_ON(NULL == eli);
 
-        eli->li_timer.data = (unsigned long)current;
-        eli->li_timer.function = ext4_lazyinode_timeout;
-
         eli->li_task = current;
         wake_up(&eli->li_wait_task);
 
@@ -2811,19 +2801,15 @@ cont_thread:
                 if (freezing(current))
                         refrigerator();
 
-                if ((time_after_eq(jiffies, next_wakeup)) ||
+                cur = jiffies;
+                if ((time_after_eq(cur, next_wakeup)) ||
                     (MAX_JIFFY_OFFSET == next_wakeup)) {
                         cond_resched();
                         continue;
                 }
 
-                eli->li_timer.expires = next_wakeup;
-                add_timer(&eli->li_timer);
-                prepare_to_wait(&eli->li_wait_daemon, &wait,
-                                TASK_INTERRUPTIBLE);
-                if (time_before(jiffies, next_wakeup))
-                        schedule();
-                finish_wait(&eli->li_wait_daemon, &wait);
+                schedule_timeout_interruptible(next_wakeup - cur);
+
                 if (kthread_should_stop()) {
                         ext4_clear_request_list();
                         goto exit_thread;
@@ -2847,12 +2833,10 @@ exit_thread:
                 goto cont_thread;
         }
         mutex_unlock(&eli->li_list_mtx);
-        del_timer_sync(&ext4_li_info->li_timer);
         eli->li_task = NULL;
         wake_up(&eli->li_wait_task);
 
         kfree(ext4_li_info);
-        ext4_lazyinit_task = NULL;
         ext4_li_info = NULL;
         mutex_unlock(&ext4_li_mtx);
 
@@ -2880,7 +2864,6 @@ static int ext4_run_lazyinit_thread(void)
         if (IS_ERR(ext4_lazyinit_task)) {
                 int err = PTR_ERR(ext4_lazyinit_task);
                 ext4_clear_request_list();
-                del_timer_sync(&ext4_li_info->li_timer);
                 kfree(ext4_li_info);
                 ext4_li_info = NULL;
                 printk(KERN_CRIT "EXT4: error %d creating inode table "
@@ -2929,9 +2912,7 @@ static int ext4_li_info_new(void)
         INIT_LIST_HEAD(&eli->li_request_list);
         mutex_init(&eli->li_list_mtx);
 
-        init_waitqueue_head(&eli->li_wait_daemon);
         init_waitqueue_head(&eli->li_wait_task);
-        init_timer(&eli->li_timer);
         eli->li_state |= EXT4_LAZYINIT_QUIT;
 
         ext4_li_info = eli;