[PATCH v2 2/4] buffer: Add lock_buffer_timeout()

[Douglas Anderson]

Add a variant of lock_buffer() that can timeout. This is useful to
avoid unbounded waits for the page lock in kcompactd.

Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v2:
- "Add lock_buffer_timeout()" new for v2.

 fs/buffer.c                 |  7 +++++++
 include/linux/buffer_head.h | 10 ++++++++++
 include/linux/wait_bit.h    | 24 ++++++++++++++++++++++++
 kernel/sched/wait_bit.c     | 14 ++++++++++++++
 4 files changed, 55 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 9e1e2add541e..fcd19c270024 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -71,6 +71,13 @@ void __lock_buffer(struct buffer_head *bh)
 }
 EXPORT_SYMBOL(__lock_buffer);
 
+int __lock_buffer_timeout(struct buffer_head *bh, unsigned long timeout)
+{
+	return wait_on_bit_lock_io_timeout(&bh->b_state, BH_Lock,
+					   TASK_UNINTERRUPTIBLE, timeout);
+}
+EXPORT_SYMBOL(__lock_buffer_timeout);
+
 void unlock_buffer(struct buffer_head *bh)
 {
 	clear_bit_unlock(BH_Lock, &bh->b_state);
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index 8f14dca5fed7..2bae464f89d5 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -237,6 +237,7 @@ struct buffer_head *alloc_buffer_head(gfp_t gfp_flags);
 void free_buffer_head(struct buffer_head * bh);
 void unlock_buffer(struct buffer_head *bh);
 void __lock_buffer(struct buffer_head *bh);
+int __lock_buffer_timeout(struct buffer_head *bh, unsigned long timeout);
 int sync_dirty_buffer(struct buffer_head *bh);
 int __sync_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
 void write_dirty_buffer(struct buffer_head *bh, blk_opf_t op_flags);
@@ -400,6 +401,15 @@ static inline void lock_buffer(struct buffer_head *bh)
 		__lock_buffer(bh);
 }
 
+static inline int lock_buffer_timeout(struct buffer_head *bh,
+				      unsigned long timeout)
+{
+	might_sleep();
+	if (!trylock_buffer(bh))
+		return __lock_buffer_timeout(bh, timeout);
+	return 0;
+}
+
 static inline struct buffer_head *getblk_unmovable(struct block_device *bdev,
 						   sector_t block,
 						   unsigned size)
diff --git a/include/linux/wait_bit.h b/include/linux/wait_bit.h
index 7725b7579b78..33f0f60b1c8c 100644
--- a/include/linux/wait_bit.h
+++ b/include/linux/wait_bit.h
@@ -30,6 +30,7 @@ void wake_up_bit(void *word, int bit);
 int out_of_line_wait_on_bit(void *word, int, wait_bit_action_f *action, unsigned int mode);
 int out_of_line_wait_on_bit_timeout(void *word, int, wait_bit_action_f *action, unsigned int mode, unsigned long timeout);
 int out_of_line_wait_on_bit_lock(void *word, int, wait_bit_action_f *action, unsigned int mode);
+int out_of_line_wait_on_bit_lock_timeout(void *word, int, wait_bit_action_f *action, unsigned int mode, unsigned long timeout);
 struct wait_queue_head *bit_waitqueue(void *word, int bit);
 extern void __init wait_bit_init(void);
 
@@ -208,6 +209,29 @@ wait_on_bit_lock_io(unsigned long *word, int bit, unsigned mode)
 	return out_of_line_wait_on_bit_lock(word, bit, bit_wait_io, mode);
 }
 
+/**
+ * wait_on_bit_lock_io_timeout - wait_on_bit_lock_io() with a timeout
+ * @word: the word being waited on, a kernel virtual address
+ * @bit: the bit of the word being waited on
+ * @mode: the task state to sleep in
+ * @timeout: the timeout in jiffies; %MAX_SCHEDULE_TIMEOUT means wait forever
+ *
+ * Returns zero if the bit was (eventually) found to be clear and was
+ * set.  Returns non-zero if a timeout happened or a signal was delivered to
+ * the process and the @mode allows that signal to wake the process.
+ */
+static inline int
+wait_on_bit_lock_io_timeout(unsigned long *word, int bit, unsigned mode,
+			    unsigned long timeout)
+{
+	might_sleep();
+	if (!test_and_set_bit(bit, word))
+		return 0;
+	return out_of_line_wait_on_bit_lock_timeout(word, bit,
+						    bit_wait_io_timeout,
+						    mode, timeout);
+}
+
 /**
  * wait_on_bit_lock_action - wait for a bit to be cleared, when wanting to set it
  * @word: the word being waited on, a kernel virtual address
diff --git a/kernel/sched/wait_bit.c b/kernel/sched/wait_bit.c
index 0b1cd985dc27..629acd1c6c79 100644
--- a/kernel/sched/wait_bit.c
+++ b/kernel/sched/wait_bit.c
@@ -118,6 +118,20 @@ int __sched out_of_line_wait_on_bit_lock(void *word, int bit,
 }
 EXPORT_SYMBOL(out_of_line_wait_on_bit_lock);
 
+int __sched out_of_line_wait_on_bit_lock_timeout(void *word, int bit,
+						 wait_bit_action_f *action,
+						 unsigned mode,
+						 unsigned long timeout)
+{
+	struct wait_queue_head *wq_head = bit_waitqueue(word, bit);
+	DEFINE_WAIT_BIT(wq_entry, word, bit);
+
+	wq_entry.key.timeout = jiffies + timeout;
+
+	return __wait_on_bit_lock(wq_head, &wq_entry, action, mode);
+}
+EXPORT_SYMBOL(out_of_line_wait_on_bit_lock_timeout);
+
 void __wake_up_bit(struct wait_queue_head *wq_head, void *word, int bit)
 {
 	struct wait_bit_key key = __WAIT_BIT_KEY_INITIALIZER(word, bit);
-- 
2.40.0.634.g4ca3ef3211-goog