linux-kernel - Re: [PATCH 10/19] USB: gadget/legacy: remove sb

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Message-ID: <7f839be1-4898-41ad-8eda-10d5a0350bdf@rowland.harvard.edu>
Date:   Wed, 13 Sep 2023 12:10:56 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Christoph Hellwig <hch@....de>
Cc:     Christian Brauner <brauner@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Damien Le Moal <dlemoal@...nel.org>,
        Naohiro Aota <naohiro.aota@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-hardening@...r.kernel.org,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 10/19] USB: gadget/legacy: remove sb_mutex

On Wed, Sep 13, 2023 at 08:10:04AM -0300, Christoph Hellwig wrote:
> Creating new a new super_block vs freeing the old one for single instance
> file systems is serialized by the wait for SB_DEAD.
> 
> Remove the superfluous sb_mutex.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---

You might mention that this is essentially a reversion of commit 
d18dcfe9860e ("USB: gadgetfs: Fix race between mounting and 
unmounting").

Alan Stern

>  drivers/usb/gadget/legacy/inode.c | 6 ------
>  1 file changed, 6 deletions(-)
> 
> diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c
> index ce9e31f3d26bcc..a203266bc0dc82 100644
> --- a/drivers/usb/gadget/legacy/inode.c
> +++ b/drivers/usb/gadget/legacy/inode.c
> @@ -229,7 +229,6 @@ static void put_ep (struct ep_data *data)
>   */
>  
>  static const char *CHIP;
> -static DEFINE_MUTEX(sb_mutex);		/* Serialize superblock operations */
>  
>  /*----------------------------------------------------------------------*/
>  
> @@ -2012,8 +2011,6 @@ gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc)
>  	struct dev_data	*dev;
>  	int		rc;
>  
> -	mutex_lock(&sb_mutex);
> -
>  	if (the_device) {
>  		rc = -ESRCH;
>  		goto Done;
> @@ -2069,7 +2066,6 @@ gadgetfs_fill_super (struct super_block *sb, struct fs_context *fc)
>  	rc = -ENOMEM;
>  
>   Done:
> -	mutex_unlock(&sb_mutex);
>  	return rc;
>  }
>  
> @@ -2092,7 +2088,6 @@ static int gadgetfs_init_fs_context(struct fs_context *fc)
>  static void
>  gadgetfs_kill_sb (struct super_block *sb)
>  {
> -	mutex_lock(&sb_mutex);
>  	kill_litter_super (sb);
>  	if (the_device) {
>  		put_dev (the_device);
> @@ -2100,7 +2095,6 @@ gadgetfs_kill_sb (struct super_block *sb)
>  	}
>  	kfree(CHIP);
>  	CHIP = NULL;
> -	mutex_unlock(&sb_mutex);
>  }
>  
>  /*----------------------------------------------------------------------*/
> -- 
> 2.39.2
>