[RFC v3 14/24] nfs: 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/nfs --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>
---
 fs/nfs/callback.c   | 4 ----
 fs/nfs/fs_context.c | 4 ++--
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 456af7d230cf..f5ba4d6bf2a7 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -77,8 +77,6 @@ nfs4_callback_svc(void *vrqstp)
 	int err;
 	struct svc_rqst *rqstp = vrqstp;
 
-	set_freezable();
-
 	while (!kthread_freezable_should_stop(NULL)) {
 
 		if (signal_pending(current))
@@ -109,8 +107,6 @@ nfs41_callback_svc(void *vrqstp)
 	int error;
 	DEFINE_WAIT(wq);
 
-	set_freezable();
-
 	while (!kthread_freezable_should_stop(NULL)) {
 
 		if (signal_pending(current))
diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
index 9bcd53d5c7d4..04753962db9a 100644
--- a/fs/nfs/fs_context.c
+++ b/fs/nfs/fs_context.c
@@ -1583,7 +1583,7 @@ struct file_system_type nfs_fs_type = {
 	.init_fs_context	= nfs_init_fs_context,
 	.parameters		= nfs_fs_parameters,
 	.kill_sb		= nfs_kill_super,
-	.fs_flags		= FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA,
+	.fs_flags		= FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA | FS_AUTOFREEZE,
 };
 MODULE_ALIAS_FS("nfs");
 EXPORT_SYMBOL_GPL(nfs_fs_type);
@@ -1595,7 +1595,7 @@ struct file_system_type nfs4_fs_type = {
 	.init_fs_context	= nfs_init_fs_context,
 	.parameters		= nfs_fs_parameters,
 	.kill_sb		= nfs_kill_super,
-	.fs_flags		= FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA,
+	.fs_flags		= FS_RENAME_DOES_D_MOVE|FS_BINARY_MOUNTDATA | FS_AUTOFREEZE,
 };
 MODULE_ALIAS_FS("nfs4");
 MODULE_ALIAS("nfs4");
-- 
2.35.1