[PATCH] init: Initialize noop_backing_dev_info early

[PATCH] init: Initialize noop_backing_dev_info early

[Jan Kara]

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@arm.com>
Reported-and-tested-by: Alexandru Elisei <alexandru.elisei@arm.com>
Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jan Kara <jack@suse.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

Re: [PATCH] init: Initialize noop_backing_dev_info early

[Christoph Hellwig]

On Wed, Jun 15, 2022 at 11:48:15PM +0200, Jan Kara wrote:
> +extern int bdi_init(struct backing_dev_info *bdi);

No need for the extern.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

And this remind me that I really want to kill noop_backing_dev_info
and just use a NULL bdi for this case eventually..

Re: [PATCH] init: Initialize noop_backing_dev_info early

[Suzuki K Poulose]

On 15/06/2022 22:48, Jan Kara wrote:
> 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@arm.com>
> Reported-and-tested-by: Alexandru Elisei <alexandru.elisei@arm.com>
> Reported-and-tested-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Jan Kara <jack@suse.cz>

Works for me too. Thanks for the proper fix


Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>


> ---
>   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;
>   

Re: [PATCH] init: Initialize noop_backing_dev_info early

[Jan Kara]

On Wed 15-06-22 23:08:22, Christoph Hellwig wrote:
> On Wed, Jun 15, 2022 at 11:48:15PM +0200, Jan Kara wrote:
> > +extern int bdi_init(struct backing_dev_info *bdi);
> 
> No need for the extern.

Yes, fixed up.

> Otherwise looks good:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Thanks for review!

> And this remind me that I really want to kill noop_backing_dev_info
> and just use a NULL bdi for this case eventually..

Yes, I'm just not sure whether the checks for bdi / wb being NULL in lots
of places will not be too annoying... But maybe you'll be able to come up
with some wrappers that will make things bearable.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR