f2fs: fix the starvation problem on cp_rwsem

This patch removes the logic previously introduced to address the starvation
on cp_rwsem.

One potential there-in bug is that we should cover the wait.list with spin_lock,
but the previous code broke this rule.

And, actually current rwsem handles this starvation issue reasonably, so that we
didn't need to do this before neither.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -18,8 +18,6 @@
 #include <linux/crc32.h>
 #include <linux/magic.h>
 #include <linux/kobject.h>
-#include <linux/wait.h>
-#include <linux/sched.h>
 
 /*
  * For mount options
@@ -360,7 +358,6 @@ struct f2fs_sb_info {
 	struct inode *meta_inode;		/* cache meta blocks */
 	struct mutex cp_mutex;			/* checkpoint procedure lock */
 	struct rw_semaphore cp_rwsem;		/* blocking FS operations */
-	wait_queue_head_t cp_wait;		/* checkpoint wait queue */
 	struct mutex node_write;		/* locking node writes */
 	struct mutex writepages;		/* mutex for writepages() */
 	int por_doing;				/* recovery is doing or not */
@@ -516,13 +513,6 @@ static inline void clear_ckpt_flags(struct f2fs_checkpoint *cp, unsigned int f)
 
 static inline void f2fs_lock_op(struct f2fs_sb_info *sbi)
 {
-	/*
-	 * If the checkpoint thread is waiting for cp_rwsem, add cuurent task
-	 * into wait list to avoid the checkpoint thread starvation
-	 */
-	while (!list_empty(&sbi->cp_rwsem.wait_list))
-		wait_event_interruptible(sbi->cp_wait,
-				list_empty(&sbi->cp_rwsem.wait_list));
 	down_read(&sbi->cp_rwsem);
 }
 
@@ -539,9 +529,6 @@ static inline void f2fs_lock_all(struct f2fs_sb_info *sbi)
 static inline void f2fs_unlock_all(struct f2fs_sb_info *sbi)
 {
 	up_write(&sbi->cp_rwsem);
-
-	/* wake up all tasks blocked by checkpoint */
-	wake_up_all(&sbi->cp_wait);
 }
 
 /*

fs/f2fs/super.c

@@ -841,7 +841,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	spin_lock_init(&sbi->stat_lock);
 	init_rwsem(&sbi->bio_sem);
 	init_rwsem(&sbi->cp_rwsem);
-	init_waitqueue_head(&sbi->cp_wait);
 	init_sb_info(sbi);
 
 	/* get an inode for meta space */