[RFC v3 19/24] jbd2: replace kthread freezing with auto fs freezing

[Luis Chamberlain]

The kernel power management now supports allowing the VFS
to handle filesystem freezing freezes and thawing. Take advantage
of that and remove the kthread freezing. This is needed so that we
properly really stop IO in flight without races after userspace
has been frozen. Without this we rely on kthread freezing and
its semantics are loose and error prone.

The filesystem therefore is in charge of properly dealing with
quiescing of the filesystem through its callbacks if it thinks
it knows better than how the VFS handles it.

The following Coccinelle rule was used as to remove the now superflous
freezer calls:

spatch --sp-file fs-freeze-cleanup.cocci --in-place --timeout 120 --dir fs/jbd2 --jobs 12 --use-gitgrep

@ remove_set_freezable @
expression time;
statement S, S2;
expression task, current;
@@

(
-       set_freezable();
|
-       if (try_to_freeze())
-               continue;
|
-       try_to_freeze();
|
-       freezable_schedule();
+       schedule();
|
-       freezable_schedule_timeout(time);
+       schedule_timeout(time);
|
-       if (freezing(task)) { S }
|
-       if (freezing(task)) { S }
-       else
	    { S2 }
|
-       freezing(current)
)

@ remove_wq_freezable @
expression WQ_E, WQ_ARG1, WQ_ARG2, WQ_ARG3, WQ_ARG4;
identifier fs_wq_fn;
@@

(
    WQ_E = alloc_workqueue(WQ_ARG1,
-                              WQ_ARG2 | WQ_FREEZABLE,
+                              WQ_ARG2,
			   ...);
|
    WQ_E = alloc_workqueue(WQ_ARG1,
-                              WQ_ARG2 | WQ_FREEZABLE | WQ_ARG3,
+                              WQ_ARG2 | WQ_ARG3,
			   ...);
|
    WQ_E = alloc_workqueue(WQ_ARG1,
-                              WQ_ARG2 | WQ_ARG3 | WQ_FREEZABLE,
+                              WQ_ARG2 | WQ_ARG3,
			   ...);
|
    WQ_E = alloc_workqueue(WQ_ARG1,
-                              WQ_ARG2 | WQ_ARG3 | WQ_FREEZABLE | WQ_ARG4,
+                              WQ_ARG2 | WQ_ARG3 | WQ_ARG4,
			   ...);
|
	    WQ_E =
-               WQ_ARG1 | WQ_FREEZABLE
+               WQ_ARG1
|
	    WQ_E =
-               WQ_ARG1 | WQ_FREEZABLE | WQ_ARG3
+               WQ_ARG1 | WQ_ARG3
|
    fs_wq_fn(
-               WQ_FREEZABLE | WQ_ARG2 | WQ_ARG3
+               WQ_ARG2 | WQ_ARG3
    )
|
    fs_wq_fn(
-               WQ_FREEZABLE | WQ_ARG2
+               WQ_ARG2
    )
|
    fs_wq_fn(
-               WQ_FREEZABLE
+               0
    )
)

@ add_auto_flag @
expression E1;
identifier fs_type;
@@

struct file_system_type fs_type = {
	.fs_flags = E1
+                   | FS_AUTOFREEZE
	,
};

Generated-by: Coccinelle SmPL
Signed-off-by: Luis Chamberlain <mcgrof at kernel.org>

Signed-off-by: Luis Chamberlain <mcgrof at kernel.org>
---
 fs/jbd2/journal.c | 54 ++++++++++++++++++-----------------------------
 1 file changed, 20 insertions(+), 34 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index e80c781731f8..99a4db5b40fc 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -169,6 +169,8 @@ static int kjournald2(void *arg)
 {
 	journal_t *journal = arg;
 	transaction_t *transaction;
+	DEFINE_WAIT(wait);
+	int should_sleep = 1;
 
 	/*
 	 * Set up an interval timer which can be used to trigger a commit wakeup
@@ -176,8 +178,6 @@ static int kjournald2(void *arg)
 	 */
 	timer_setup(&journal->j_commit_timer, commit_timeout, 0);
 
-	set_freezable();
-
 	/* Record that the journal thread is running */
 	journal->j_task = current;
 	wake_up(&journal->j_wait_done_commit);
@@ -212,41 +212,27 @@ static int kjournald2(void *arg)
 	}
 
 	wake_up(&journal->j_wait_done_commit);
-	if (freezing(current)) {
-		/*
-		 * The simpler the better. Flushing journal isn't a
-		 * good idea, because that depends on threads that may
-		 * be already stopped.
-		 */
-		jbd2_debug(1, "Now suspending kjournald2\n");
+	/*
+	 * We assume on resume that commits are already there,
+	 * so we don't sleep
+	 */
+
+	prepare_to_wait(&journal->j_wait_commit, &wait,
+			TASK_INTERRUPTIBLE);
+	if (journal->j_commit_sequence != journal->j_commit_request)
+		should_sleep = 0;
+	transaction = journal->j_running_transaction;
+	if (transaction && time_after_eq(jiffies,
+					transaction->t_expires))
+		should_sleep = 0;
+	if (journal->j_flags & JBD2_UNMOUNT)
+		should_sleep = 0;
+	if (should_sleep) {
 		write_unlock(&journal->j_state_lock);
-		try_to_freeze();
+		schedule();
 		write_lock(&journal->j_state_lock);
-	} else {
-		/*
-		 * We assume on resume that commits are already there,
-		 * so we don't sleep
-		 */
-		DEFINE_WAIT(wait);
-		int should_sleep = 1;
-
-		prepare_to_wait(&journal->j_wait_commit, &wait,
-				TASK_INTERRUPTIBLE);
-		if (journal->j_commit_sequence != journal->j_commit_request)
-			should_sleep = 0;
-		transaction = journal->j_running_transaction;
-		if (transaction && time_after_eq(jiffies,
-						transaction->t_expires))
-			should_sleep = 0;
-		if (journal->j_flags & JBD2_UNMOUNT)
-			should_sleep = 0;
-		if (should_sleep) {
-			write_unlock(&journal->j_state_lock);
-			schedule();
-			write_lock(&journal->j_state_lock);
-		}
-		finish_wait(&journal->j_wait_commit, &wait);
 	}
+	finish_wait(&journal->j_wait_commit, &wait);
 
 	jbd2_debug(1, "kjournald2 wakes\n");
 
-- 
2.35.1