linux-kernel - Re: [PATCH] jfs: makes diUnmount/diMount in jfs_mount

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Date:   Thu, 10 Nov 2022 15:47:10 -0600
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Oleg Kanatov <okanatov@...il.com>
Cc:     Oleg Kanatov <okanatov@...ralinux.ru>,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        lvc-project@...uxtesting.org
Subject: Re: [PATCH] jfs: makes diUnmount/diMount in jfs_mount_rw atomic

Applied with trivial changes. I cleaned up the commit message a little 
and removed a couple blank lines.

Thanks!

On 10/28/22 7:22AM, Oleg Kanatov wrote:
> jfs_mount_rw can call diUnmount and then diMount. These calls
> change the imap pointer.
> In case JFS filesystem is mounted on root (/), between these two
> calls there may be calls of function jfs_lookup().
> The jfs_lookup() function calls jfs_iget(), which, in its turn,
> calls diRead(). The latter references the imap pointer.
> That may cause diRead() to refer to a pointer "freed" in
> diUnmount().
> This commit makes calls diUnmount()/diMount() be atomic so that
> nothing will read the imap pointer until the whole remount is
> completed.
> 
> Signed-off-by: Oleg Kanatov <okanatov@...il.com>
> ---
>   fs/jfs/jfs_imap.c  | 2 +-
>   fs/jfs/jfs_mount.c | 6 ++++++
>   2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_imap.c b/fs/jfs/jfs_imap.c
> index 799d3837e7c2..390cbfce391f 100644
> --- a/fs/jfs/jfs_imap.c
> +++ b/fs/jfs/jfs_imap.c
> @@ -310,8 +310,8 @@ int diRead(struct inode *ip)
>   	iagno = INOTOIAG(ip->i_ino);
>   
>   	/* read the iag */
> -	imap = JFS_IP(ipimap)->i_imap;
>   	IREAD_LOCK(ipimap, RDWRLOCK_IMAP);
> +	imap = JFS_IP(ipimap)->i_imap;
>   	rc = diIAGRead(imap, iagno, &mp);
>   	IREAD_UNLOCK(ipimap);
>   	if (rc) {
> diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c
> index 48d1f70f786c..972b9ff18723 100644
> --- a/fs/jfs/jfs_mount.c
> +++ b/fs/jfs/jfs_mount.c
> @@ -234,12 +234,18 @@ int jfs_mount_rw(struct super_block *sb, int remount)
>   
>   		truncate_inode_pages(sbi->ipimap->i_mapping, 0);
>   		truncate_inode_pages(sbi->ipbmap->i_mapping, 0);
> +
> +		IWRITE_LOCK(sbi->ipimap, RDWRLOCK_IMAP);
> +
>   		diUnmount(sbi->ipimap, 1);
>   		if ((rc = diMount(sbi->ipimap))) {
> +			IWRITE_UNLOCK(sbi->ipimap);
>   			jfs_err("jfs_mount_rw: diMount failed!");
>   			return rc;
>   		}
>   
> +		IWRITE_UNLOCK(sbi->ipimap);
> +
>   		dbUnmount(sbi->ipbmap, 1);
>   		if ((rc = dbMount(sbi->ipbmap))) {
>   			jfs_err("jfs_mount_rw: dbMount failed!");