linux-kernel - Re: [PATCH] init: Initialize noop_backing_dev

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Date:   Thu, 16 Jun 2022 09:10:23 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-mm@...ck.org, Guenter Roeck <linux@...ck-us.net>,
        Alexandru Elisei <alexandru.elisei@....com>
Subject: Re: [PATCH] init: Initialize noop_backing_dev_info early

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@....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>

Works for me too. Thanks for the proper fix


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