linux-kernel - [PATCH 1/3] ext4: replace kthread freezing with auto fs freezing

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Message-Id: <20230508011927.4036707-2-mcgrof@kernel.org>
Date:   Sun,  7 May 2023 18:19:25 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     hch@...radead.org, djwong@...nel.org, sandeen@...deen.net,
        song@...nel.org, rafael@...nel.org, gregkh@...uxfoundation.org,
        viro@...iv.linux.org.uk, jack@...e.cz, jikos@...nel.org,
        bvanassche@....org, ebiederm@...ssion.com
Cc:     mchehab@...nel.org, keescook@...omium.org, p.raghav@...sung.com,
        da.gomez@...sung.com, linux-fsdevel@...r.kernel.org,
        kernel@...force.de, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>
Subject: [PATCH 1/3] ext4: replace kthread freezing with auto fs freezing

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 superfluous
freezer calls:

make coccicheck MODE=patch SPFLAGS="--in-place --no-show-diff" COCCI=./fs-freeze-cleanup.cocci M=fs/ext4

virtual patch

@ 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@...nel.org>
---
 fs/ext4/super.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d39f386e9baf..1f436938d8be 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -136,7 +136,7 @@ static struct file_system_type ext2_fs_type = {
 	.init_fs_context	= ext4_init_fs_context,
 	.parameters		= ext4_param_specs,
 	.kill_sb		= kill_block_super,
-	.fs_flags		= FS_REQUIRES_DEV,
+	.fs_flags		= FS_REQUIRES_DEV | FS_AUTOFREEZE,
 };
 MODULE_ALIAS_FS("ext2");
 MODULE_ALIAS("ext2");
@@ -152,7 +152,7 @@ static struct file_system_type ext3_fs_type = {
 	.init_fs_context	= ext4_init_fs_context,
 	.parameters		= ext4_param_specs,
 	.kill_sb		= kill_block_super,
-	.fs_flags		= FS_REQUIRES_DEV,
+	.fs_flags		= FS_REQUIRES_DEV | FS_AUTOFREEZE,
 };
 MODULE_ALIAS_FS("ext3");
 MODULE_ALIAS("ext3");
@@ -3790,7 +3790,6 @@ static int ext4_lazyinit_thread(void *arg)
 	unsigned long next_wakeup, cur;
 
 	BUG_ON(NULL == eli);
-	set_freezable();
 
 cont_thread:
 	while (true) {
@@ -3842,8 +3841,6 @@ static int ext4_lazyinit_thread(void *arg)
 		}
 		mutex_unlock(&eli->li_list_mtx);
 
-		try_to_freeze();
-
 		cur = jiffies;
 		if ((time_after_eq(cur, next_wakeup)) ||
 		    (MAX_JIFFY_OFFSET == next_wakeup)) {
@@ -7245,7 +7242,7 @@ static struct file_system_type ext4_fs_type = {
 	.init_fs_context	= ext4_init_fs_context,
 	.parameters		= ext4_param_specs,
 	.kill_sb		= kill_block_super,
-	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
+	.fs_flags		= FS_REQUIRES_DEV | FS_ALLOW_IDMAP | FS_AUTOFREEZE,
 };
 MODULE_ALIAS_FS("ext4");
 
-- 
2.39.2