threads/141198: src/lib/libc/stdio does not properly initialize mutexes

[John Baldwin]

On Monday 07 December 2009 8:50:37 am John Baldwin wrote:
> On Saturday 05 December 2009 3:34:41 pm Jeremy Huddleston wrote:
> > 
> > >Number:         141198
> > >Category:       threads
> > >Synopsis:       src/lib/libc/stdio does not properly initialize mutexes
> > >Confidential:   no
> > >Severity:       non-critical
> > >Priority:       low
> > >Responsible:    freebsd-threads
> > >State:          open
> > >Quarter:        
> > >Keywords:       
> > >Date-Required:
> > >Class:          sw-bug
> > >Submitter-Id:   current-users
> > >Arrival-Date:   Sat Dec 05 20:40:01 UTC 2009
> > >Closed-Date:
> > >Last-Modified:
> > >Originator:     Jeremy Huddleston
> > >Release:        8.0
> > >Organization:
> > Apple
> > >Environment:
> > NA
> > >Description:
> > libc/stdio assumes PTHREAD_MUTEX_INITIALIZER is NULL (which it is in 
> FreeBSD), but this makes the code not as portable.
> > 
> > Earlier versions of stdio did properly initialize the lock to 
> PTHREAD_MUTEX_INITIALIZER in INITEXTRA() when it was part of the _extra 
> extension substructure.
> 
> This is my fault.  I suspect it was more an error of omission on my part than 
> assuming the default value of PTHREAD_MUTEX_INITIALIZER. :)  Hmm, so I 
> reviewed the change that removed INITEXTRA() and all the places it was used to 
> construct a 'fake' FILE object it was passed to an internal stdio routine that 
> did not use locking.  One thing I do see that is an old bug is that the three 
> static FILE structures used for stdin, stdout, and stderr have never had their 
> internal locks properly initialized.  Also, it seems __sfp() never initializes 
> fp->_lock at all.  Oh, it gets set to NULL via 'empty' in moreglue().  That is 
> also an old bug.  I think this will fix those problems:
> 
> Index: stdio/findfp.c
> ===================================================================
> --- stdio/findfp.c	(revision 199969)
> +++ stdio/findfp.c	(working copy)
> @@ -61,6 +61,7 @@
>  	._read = __sread,		\
>  	._seek = __sseek,		\
>  	._write = __swrite,		\
> +	._fl_mutex = PTHREAD_MUTEX_INITIALIZER, \
>  }
>  				/* the usual - (stdin + stdout + stderr) */
>  static FILE usual[FOPEN_MAX - 3];
> @@ -96,7 +97,7 @@
>  	int n;
>  {
>  	struct glue *g;
> -	static FILE empty;
> +	static FILE empty = { ._fl_mutex = PTHREAD_MUTEX_INITIALIZER };
>  	FILE *p;
>  
>  	g = (struct glue *)malloc(sizeof(*g) + ALIGNBYTES + n * sizeof(FILE));
> @@ -154,7 +155,7 @@
>  	fp->_ub._size = 0;
>  	fp->_lb._base = NULL;	/* no line buffer */
>  	fp->_lb._size = 0;
> -/*	fp->_lock = NULL; */	/* once set always set (reused) */
> +/*	fp->_fl_mutex = NULL; */ /* once set always set (reused) */
>  	fp->_orientation = 0;
>  	memset(&fp->_mbstate, 0, sizeof(mbstate_t));
>  	return (fp);

Does this patch address the concerns?

-- 
John Baldwin