linux-kernel - Re: [PATCH v3] fs/locks: print full locks information

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Message-ID: <f8c7a7fe8ee7fc1f1a36f35f38cc653d167b25a1.camel@kernel.org>
Date:   Tue, 09 Mar 2021 08:37:21 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     Luo Longjun <luolongjun@...wei.com>, viro@...iv.linux.org.uk,
        bfields@...ldses.org
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        sangyan@...wei.com, luchunhua@...wei.com
Subject: Re: [PATCH v3] fs/locks: print full locks information

On Thu, 2021-02-25 at 22:58 -0500, Luo Longjun wrote:
> Commit fd7732e033e3 ("fs/locks: create a tree of dependent requests.")
> has put blocked locks into a tree.
> 
> So, with a for loop, we can't check all locks information.
> 
> To solve this problem, we should traverse the tree.
> 
> Signed-off-by: Luo Longjun <luolongjun@...wei.com>
> ---
>  fs/locks.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 56 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index 99ca97e81b7a..ecaecd1f1b58 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -2828,7 +2828,7 @@ struct locks_iterator {
>  };
>  
> 
> 
> 
>  static void lock_get_status(struct seq_file *f, struct file_lock *fl,
> -			    loff_t id, char *pfx)
> +			    loff_t id, char *pfx, int repeat)
>  {
>  	struct inode *inode = NULL;
>  	unsigned int fl_pid;
> @@ -2844,7 +2844,11 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>  	if (fl->fl_file != NULL)
>  		inode = locks_inode(fl->fl_file);
>  
> 
> 
> 
> -	seq_printf(f, "%lld:%s ", id, pfx);
> +	seq_printf(f, "%lld: ", id);
> +
> +	if (repeat)
> +		seq_printf(f, "%*s", repeat - 1 + (int)strlen(pfx), pfx);

Shouldn't that be "%.*s" ?

Also, isn't this likely to end up walking past the end of "pfx" (or even
ending up at an address before the buffer)? You have this below:

    lock_get_status(f, fl, *id, "", 0);

...so the "length" value you're passing into the format there is going
to be -1. It also seems like if you get a large "level" value in
locks_show, then you'll end up with a length that is much longer than
the actual string.

> +
>  	if (IS_POSIX(fl)) {
>  		if (fl->fl_flags & FL_ACCESS)
>  			seq_puts(f, "ACCESS");
> @@ -2906,21 +2910,64 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
>  	}
>  }
>  
> 
> 
> 
> +static struct file_lock *get_next_blocked_member(struct file_lock *node)
> +{
> +	struct file_lock *tmp;
> +
> +	/* NULL node or root node */
> +	if (node == NULL || node->fl_blocker == NULL)
> +		return NULL;
> +
> +	/* Next member in the linked list could be itself */
> +	tmp = list_next_entry(node, fl_blocked_member);
> +	if (list_entry_is_head(tmp, &node->fl_blocker->fl_blocked_requests, fl_blocked_member)
> +		|| tmp == node) {
> +		return NULL;
> +	}
> +
> +	return tmp;
> +}
> +
>  static int locks_show(struct seq_file *f, void *v)
>  {
>  	struct locks_iterator *iter = f->private;
> -	struct file_lock *fl, *bfl;
> +	struct file_lock *cur, *tmp;
>  	struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
> +	int level = 0;
>  
> 
> 
> 
> -	fl = hlist_entry(v, struct file_lock, fl_link);
> +	cur = hlist_entry(v, struct file_lock, fl_link);
>  
> 
> 
> 
> -	if (locks_translate_pid(fl, proc_pidns) == 0)
> +	if (locks_translate_pid(cur, proc_pidns) == 0)
>  		return 0;
>  
> 
> 
> 
> -	lock_get_status(f, fl, iter->li_pos, "");
> +	/* View this crossed linked list as a binary tree, the first member of fl_blocked_requests
> +	 * is the left child of current node, the next silibing in fl_blocked_member is the
> +	 * right child, we can alse get the parent of current node from fl_blocker, so this
> +	 * question becomes traversal of a binary tree
> +	 */
> +	while (cur != NULL) {
> +		if (level)
> +			lock_get_status(f, cur, iter->li_pos, "-> ", level);
> +		else
> +			lock_get_status(f, cur, iter->li_pos, "", level);
>  
> 
> 
> 
> -	list_for_each_entry(bfl, &fl->fl_blocked_requests, fl_blocked_member)
> -		lock_get_status(f, bfl, iter->li_pos, " ->");
> +		if (!list_empty(&cur->fl_blocked_requests)) {
> +			/* Turn left */
> +			cur = list_first_entry_or_null(&cur->fl_blocked_requests,
> +				struct file_lock, fl_blocked_member);
> +			level++;
> +		} else {
> +			/* Turn right */
> +			tmp = get_next_blocked_member(cur);
> +			/* Fall back to parent node */
> +			while (tmp == NULL && cur->fl_blocker != NULL) {
> +				cur = cur->fl_blocker;
> +				level--;
> +				tmp = get_next_blocked_member(cur);
> +			}
> +			cur = tmp;
> +		}
> +	}
>  
> 
> 
> 
>  	return 0;
>  }
> @@ -2941,7 +2988,7 @@ static void __show_fd_locks(struct seq_file *f,
>  
> 
> 
> 
>  		(*id)++;
>  		seq_puts(f, "lock:\t");
> -		lock_get_status(f, fl, *id, "");
> +		lock_get_status(f, fl, *id, "", 0);
>  	}
>  }
>  
> 
> 
> 

-- 
Jeff Layton <jlayton@...nel.org>