Date: Mon, 7 Dec 2009 08:50:37 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-threads@freebsd.org Cc: freebsd-gnats-submit@freebsd.org, Jeremy Huddleston <jeremyhu@apple.com> Subject: Re: threads/141198: src/lib/libc/stdio does not properly initialize mutexes Message-ID: <200912070850.37112.jhb@freebsd.org> In-Reply-To: <200912052034.nB5KYfaY000395@www.freebsd.org> References: <200912052034.nB5KYfaY000395@www.freebsd.org>
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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
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