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

[John Baldwin]

The following reply was made to PR threads/141198; it has been noted by GNATS.

From: John Baldwin <jhb at freebsd.org>
To: freebsd-threads at freebsd.org
Cc: Jeremy Huddleston <jeremyhu at apple.com>,
 freebsd-gnats-submit at freebsd.org
Subject: Re: threads/141198: src/lib/libc/stdio does not properly initialize mutexes
Date: Mon, 7 Dec 2009 08:50:37 -0500

 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);
 
 
 -- 
 John Baldwin