Re: [PATCH] xfs_repair: fix progress reporting

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, May 18, 2020 at 05:35:33PM -0500, Eric Sandeen wrote:
> Long ago, a young developer tried to fix a segfault in xfs_repair where
> a short progress reporting interval could cause a timer to go off and try
> to print a progress mesage before any had been properly set up because
> we were still busy zeroing the log, and a NULL pointer dereference
> ensued.
> 
> That young developer got it wrong, and completely broke progress
> reporting, because the change caused us to exit early from the pthread
> start routine, and not initialize the progress timer at all.
> 
> That developer is now slightly older and wiser, and finally realizes that
> the simple and correct solution here is to initialize the message format
> to the first one in the list, so that we will be ready to go with a
> progress message no matter when the first timer goes off.
> 
> Reported-by: Leonardo Vaz <lvaz@redhat.com>
> Fixes: 7f2d6b811755 ("xfs_repair: avoid segfault if reporting progre...")
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> It might be nice to add progress reporting for the log zeroing, but that
> requires renumbering all these macros, and we don't/can't actually get
> any fine-grained progress at all, so probably not worth it.
> 
> diff --git a/repair/progress.c b/repair/progress.c
> index 5ee08229..d7baa606 100644
> --- a/repair/progress.c
> +++ b/repair/progress.c
> @@ -125,7 +125,11 @@ init_progress_rpt (void)
>  	 */
>  
>  	pthread_mutex_init(&global_msgs.mutex, NULL);
> -	global_msgs.format = NULL;
> +	/*
> +	 * Ensure the format string is not NULL in case the first timer
> +	 * goes off before any stage calls set_progress_msg() to set it.
> +	 */
> +	global_msgs.format = &progress_rpt_reports[0];

Hmm so does that mean the first progress report could be for "scanning
freespace"?

Or could you append a new entry to progress_rpt_reports for "getting my
shit together and moving out of my parents basement" and initialize it
to that?

--D

>  	global_msgs.count = glob_agcount;
>  	global_msgs.interval = report_interval;
>  	global_msgs.done   = prog_rpt_done;
> @@ -171,10 +175,6 @@ progress_rpt_thread (void *p)
>  	msg_block_t *msgp = (msg_block_t *)p;
>  	uint64_t percent;
>  
> -	/* It's possible to get here very early w/ no progress msg set */
> -	if (!msgp->format)
> -		return NULL;
> -
>  	if ((msgbuf = (char *)malloc(DURATION_BUF_SIZE)) == NULL)
>  		do_error (_("progress_rpt: cannot malloc progress msg buffer\n"));
>  
>