Fix the handle locking in stdio
Fix the handle locking in stdio to use flockfile/funlockfile
internally when and where required. Macros in <stdio.h> are updated
to automatically call the underlying functions when the process is
threaded to obtain the necessary locking. A private mutex is added
to protect __sglue, the internal list of FILE handles, and another
to protect the one-time initialization. Some routines in libc that
use getc() change to use getc_unlocked() as they're either protected
by their own lock or aren't thread-safe routines anyway.
Based on OpenBSD change by guenther@openbsd.org
http://www.mail-archive.com/source-changes@cvs.openbsd.org/msg01015.html
Bug: 3446659
Change-Id: Ie82116e358c541718d6709ec45ca6796be5a007b
diff --git a/libc/stdio/findfp.c b/libc/stdio/findfp.c
index 1d0f9c5..a659c87 100644
--- a/libc/stdio/findfp.c
+++ b/libc/stdio/findfp.c
@@ -39,6 +39,7 @@
#include <string.h>
#include "local.h"
#include "glue.h"
+#include "thread_private.h"
int __sdidinit;
@@ -54,6 +55,8 @@
static FILE usual[FOPEN_MAX - 3];
static struct __sfileext usualext[FOPEN_MAX - 3];
static struct glue uglue = { 0, FOPEN_MAX - 3, usual };
+static struct glue *lastglue = &uglue;
+_THREAD_PRIVATE_MUTEX(__sfp_mutex);
static struct __sfileext __sFext[3];
FILE __sF[3] = {
@@ -104,16 +107,25 @@
if (!__sdidinit)
__sinit();
- for (g = &__sglue;; g = g->next) {
+
+ _THREAD_PRIVATE_MUTEX_LOCK(__sfp_mutex);
+ for (g = &__sglue; g != NULL; g = g->next) {
for (fp = g->iobs, n = g->niobs; --n >= 0; fp++)
if (fp->_flags == 0)
goto found;
- if (g->next == NULL && (g->next = moreglue(NDYNAMIC)) == NULL)
- break;
}
- return (NULL);
+
+ /* release lock while mallocing */
+ _THREAD_PRIVATE_MUTEX_UNLOCK(__sfp_mutex);
+ if ((g = moreglue(NDYNAMIC)) == NULL)
+ return (NULL);
+ _THREAD_PRIVATE_MUTEX_LOCK(__sfp_mutex);
+ lastglue->next = g;
+ lastglue = g;
+ fp = g->iobs;
found:
fp->_flags = 1; /* reserve this slot; caller sets real flags */
+ _THREAD_PRIVATE_MUTEX_UNLOCK(__sfp_mutex);
fp->_p = NULL; /* no current pointer */
fp->_w = 0; /* nothing to read or write */
fp->_r = 0;
@@ -144,8 +156,12 @@
n = getdtablesize() - FOPEN_MAX + 20; /* 20 for slop. */
for (g = &__sglue; (n -= g->niobs) > 0 && g->next; g = g->next)
/* void */;
- if (n > 0)
- g->next = moreglue(n);
+ if (n > 0 && ((g = moreglue(n)) != NULL)) {
+ _THREAD_PRIVATE_MUTEX_LOCK(__sfp_mutex);
+ lastglue->next = g;
+ lastglue = g;
+ _THREAD_PRIVATE_MUTEX_UNLOCK(__sfp_mutex);
+ }
}
#endif
@@ -170,12 +186,18 @@
void
__sinit(void)
{
+ _THREAD_PRIVATE_MUTEX(__sinit_mutex);
int i;
+ _THREAD_PRIVATE_MUTEX_LOCK(__sinit_mutex);
+ if (__sdidinit)
+ goto out; /* bail out if caller lost the race */
for (i = 0; i < FOPEN_MAX - 3; i++) {
_FILEEXT_SETUP(usual+i, usualext+i);
}
/* make sure we clean up on exit */
__atexit_register_cleanup(_cleanup); /* conservative */
__sdidinit = 1;
+out:
+ _THREAD_PRIVATE_MUTEX_UNLOCK(__sinit_mutex);
}