linux-kernel - [PATCH] init: Initialize noop_backing_dev

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Date:   Wed, 15 Jun 2022 23:48:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-mm@...ck.org>, Suzuki K Poulose <suzuki.poulose@....com>,
        Guenter Roeck <linux@...ck-us.net>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Jan Kara <jack@...e.cz>
Subject: [PATCH] init: Initialize noop_backing_dev_info early

noop_backing_dev_info is used by superblocks of various
pseudofilesystems such as kdevtmpfs. After commit 10e14073107d
("writeback: Fix inode->i_io_list not be protected by inode->i_lock
error") this broke because __mark_inode_dirty() started to access more
fields from noop_backing_dev_info and this led to crashes inside
locked_inode_to_wb_and_lock_list() called from __mark_inode_dirty().
Fix the problem by initializing noop_backing_dev_info before the
filesystems get mounted.

Fixes: 10e14073107d ("writeback: Fix inode->i_io_list not be protected by inode->i_lock error")
Reported-by: Suzuki K Poulose <suzuki.poulose@....com>
Reported-and-tested-by: Alexandru Elisei <alexandru.elisei@....com>
Reported-and-tested-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Jan Kara <jack@...e.cz>
---
 drivers/base/init.c         |  2 ++
 include/linux/backing-dev.h |  2 ++
 mm/backing-dev.c            | 11 ++---------
 3 files changed, 6 insertions(+), 9 deletions(-)

Since this bug prevents some machines from booting, I plan to push this patch
to Linus unless someone objects soon... Review is welcome :).

diff --git a/drivers/base/init.c b/drivers/base/init.c
index d8d0fe687111..397eb9880cec 100644
--- a/drivers/base/init.c
+++ b/drivers/base/init.c
@@ -8,6 +8,7 @@
 #include <linux/init.h>
 #include <linux/memory.h>
 #include <linux/of.h>
+#include <linux/backing-dev.h>
 
 #include "base.h"
 
@@ -20,6 +21,7 @@
 void __init driver_init(void)
 {
 	/* These are the core pieces */
+	bdi_init(&noop_backing_dev_info);
 	devtmpfs_init();
 	devices_init();
 	buses_init();
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 2bd073fa6bb5..f0baef68f90f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -119,6 +119,8 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 
 extern struct backing_dev_info noop_backing_dev_info;
 
+extern int bdi_init(struct backing_dev_info *bdi);
+
 /**
  * writeback_in_progress - determine whether there is writeback in progress
  * @wb: bdi_writeback of interest
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index ff60bd7d74e0..95550b8fa7fe 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -231,20 +231,13 @@ static __init int bdi_class_init(void)
 }
 postcore_initcall(bdi_class_init);
 
-static int bdi_init(struct backing_dev_info *bdi);
-
 static int __init default_bdi_init(void)
 {
-	int err;
-
 	bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |
 				 WQ_SYSFS, 0);
 	if (!bdi_wq)
 		return -ENOMEM;
-
-	err = bdi_init(&noop_backing_dev_info);
-
-	return err;
+	return 0;
 }
 subsys_initcall(default_bdi_init);
 
@@ -781,7 +774,7 @@ static void cgwb_remove_from_bdi_list(struct bdi_writeback *wb)
 
 #endif	/* CONFIG_CGROUP_WRITEBACK */
 
-static int bdi_init(struct backing_dev_info *bdi)
+int bdi_init(struct backing_dev_info *bdi)
 {
 	int ret;
 
-- 
2.35.3