Re: [PATCH] mm,fs: Split dump_mapping() out from dump_page()

[Michal Hocko <mhocko@suse.com>]

On Sun 21-11-21 12:10:56, Matthew Wilcox wrote:
> dump_mapping() is a big chunk of dump_page(), and it'd be handy to be
> able to call it when we don't have a struct page.  Split it out and move
> it to fs/inode.c.  Take the opportunity to simplify some of the debug
> messages a little.

Makes sense. I haven't checked the head files inclusion side of this but
I suspect mm heads do include uaccess.h. Not sure inode.c does as well.

> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  fs/inode.c         | 49 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/fs.h |  1 +
>  mm/debug.c         | 52 ++--------------------------------------------
>  3 files changed, 52 insertions(+), 50 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index bdfbd5962f2b..67758b2b702f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -522,6 +522,55 @@ void __remove_inode_hash(struct inode *inode)
>  }
>  EXPORT_SYMBOL(__remove_inode_hash);
>  
> +void dump_mapping(const struct address_space *mapping)
> +{
> +	struct inode *host;
> +	const struct address_space_operations *a_ops;
> +	struct hlist_node *dentry_first;
> +	struct dentry *dentry_ptr;
> +	struct dentry dentry;
> +	unsigned long ino;
> +
> +	/*
> +	 * If mapping is an invalid pointer, we don't want to crash
> +	 * accessing it, so probe everything depending on it carefully.
> +	 */
> +	if (get_kernel_nofault(host, &mapping->host) ||
> +	    get_kernel_nofault(a_ops, &mapping->a_ops)) {
> +		pr_warn("invalid mapping:%px\n", mapping);
> +		return;
> +	}
> +
> +	if (!host) {
> +		pr_warn("aops:%ps\n", a_ops);
> +		return;
> +	}
> +
> +	if (get_kernel_nofault(dentry_first, &host->i_dentry.first) ||
> +	    get_kernel_nofault(ino, &host->i_ino)) {
> +		pr_warn("aops:%ps invalid inode:%px\n", a_ops, host);
> +		return;
> +	}
> +
> +	if (!dentry_first) {
> +		pr_warn("aops:%ps ino:%lx\n", a_ops, ino);
> +		return;
> +	}
> +
> +	dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
> +	if (get_kernel_nofault(dentry, dentry_ptr)) {
> +		pr_warn("aops:%ps ino:%lx invalid dentry:%px\n",
> +				a_ops, ino, dentry_ptr);
> +		return;
> +	}
> +
> +	/*
> +	 * if dentry is corrupted, the %pd handler may still crash,
> +	 * but it's unlikely that we reach here with a corrupt mapping
> +	 */
> +	pr_warn("aops:%ps ino:%lx dentry name:\"%pd\"\n", a_ops, ino, &dentry);
> +}
> +
>  void clear_inode(struct inode *inode)
>  {
>  	/*
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d6a4eb6cf825..acaad2b0d5b9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3149,6 +3149,7 @@ extern void unlock_new_inode(struct inode *);
>  extern void discard_new_inode(struct inode *);
>  extern unsigned int get_next_ino(void);
>  extern void evict_inodes(struct super_block *sb);
> +void dump_mapping(const struct address_space *);
>  
>  /*
>   * Userspace may rely on the the inode number being non-zero. For example, glibc
> diff --git a/mm/debug.c b/mm/debug.c
> index fae0f81ad831..b3ebfab21cb3 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -110,56 +110,8 @@ static void __dump_page(struct page *page)
>  		type = "ksm ";
>  	else if (PageAnon(page))
>  		type = "anon ";
> -	else if (mapping) {
> -		struct inode *host;
> -		const struct address_space_operations *a_ops;
> -		struct hlist_node *dentry_first;
> -		struct dentry *dentry_ptr;
> -		struct dentry dentry;
> -		unsigned long ino;
> -
> -		/*
> -		 * mapping can be invalid pointer and we don't want to crash
> -		 * accessing it, so probe everything depending on it carefully
> -		 */
> -		if (get_kernel_nofault(host, &mapping->host) ||
> -		    get_kernel_nofault(a_ops, &mapping->a_ops)) {
> -			pr_warn("failed to read mapping contents, not a valid kernel address?\n");
> -			goto out_mapping;
> -		}
> -
> -		if (!host) {
> -			pr_warn("aops:%ps\n", a_ops);
> -			goto out_mapping;
> -		}
> -
> -		if (get_kernel_nofault(dentry_first, &host->i_dentry.first) ||
> -		    get_kernel_nofault(ino, &host->i_ino)) {
> -			pr_warn("aops:%ps with invalid host inode %px\n",
> -					a_ops, host);
> -			goto out_mapping;
> -		}
> -
> -		if (!dentry_first) {
> -			pr_warn("aops:%ps ino:%lx\n", a_ops, ino);
> -			goto out_mapping;
> -		}
> -
> -		dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
> -		if (get_kernel_nofault(dentry, dentry_ptr)) {
> -			pr_warn("aops:%ps ino:%lx with invalid dentry %px\n",
> -					a_ops, ino, dentry_ptr);
> -		} else {
> -			/*
> -			 * if dentry is corrupted, the %pd handler may still
> -			 * crash, but it's unlikely that we reach here with a
> -			 * corrupted struct page
> -			 */
> -			pr_warn("aops:%ps ino:%lx dentry name:\"%pd\"\n",
> -					a_ops, ino, &dentry);
> -		}
> -	}
> -out_mapping:
> +	else if (mapping)
> +		dump_mapping(mapping);
>  	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
>  
>  	pr_warn("%sflags: %#lx(%pGp)%s\n", type, head->flags, &head->flags,
> -- 
> 2.33.0

-- 
Michal Hocko
SUSE Labs