tlib9/fmt: avoid racy access to installed fmt formats - plan9port - [fork] Plan 9 from user space
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DIR LICENSE
---
DIR commit 7ba9f9467d95fa8d05bb04d36fd4c602e497f529
DIR parent d96e9e5dc39a356febed132703e46bf73bac6850
HTML Author: Russ Cox <rsc@swtch.com>
Date: Mon, 13 Jan 2020 11:41:37 -0500
lib9/fmt: avoid racy access to installed fmt formats
Diffstat:
M src/lib9/fmt/fmt.c | 35 +++++++++++++++++++------------
M src/lib9/fmt/fmtdef.h | 6 ++++--
M src/lib9/fmt/fmtlock.c | 14 ++++++++++++--
M src/lib9/fmtlock2.c | 22 +++++++++++++++++-----
4 files changed, 55 insertions(+), 22 deletions(-)
---
DIR diff --git a/src/lib9/fmt/fmt.c b/src/lib9/fmt/fmt.c
t@@ -72,7 +72,7 @@ static Convfmt knownfmt[] = {
int (*fmtdoquote)(int);
/*
- * __fmtlock() must be set
+ * __fmtwlock() must be set
*/
static int
__fmtinstall(int c, Fmts f)
t@@ -106,34 +106,43 @@ fmtinstall(int c, int (*f)(Fmt*))
{
int ret;
- __fmtlock();
+ __fmtwlock();
ret = __fmtinstall(c, f);
- __fmtunlock();
+ __fmtwunlock();
return ret;
}
static Fmts
fmtfmt(int c)
{
- Convfmt *p, *ep;
+ Convfmt *p, *ep, *kp;
+ /* conflict-free check - common case */
+ __fmtrlock();
ep = &fmtalloc.fmt[fmtalloc.nfmt];
for(p=fmtalloc.fmt; p<ep; p++)
if(p->c == c){
- while(p->fmt == nil) /* loop until value is updated */
- ;
+ __fmtrunlock();
return p->fmt;
}
+ __fmtrunlock();
/* is this a predefined format char? */
- __fmtlock();
- for(p=knownfmt; p->c; p++)
- if(p->c == c){
- __fmtinstall(p->c, p->fmt);
- __fmtunlock();
- return p->fmt;
+ for(kp=knownfmt; kp->c; kp++){
+ if(kp->c == c){
+ __fmtwlock();
+ /* double-check fmtinstall didn't happen */
+ for(p=fmtalloc.fmt; p<ep; p++){
+ if(p->c == c){
+ __fmtwunlock();
+ return p->fmt;
+ }
+ }
+ __fmtinstall(kp->c, kp->fmt);
+ __fmtwunlock();
+ return kp->fmt;
}
- __fmtunlock();
+ }
return __badfmt;
}
DIR diff --git a/src/lib9/fmt/fmtdef.h b/src/lib9/fmt/fmtdef.h
t@@ -33,11 +33,13 @@ int __fmtFdFlush(Fmt *f);
int __fmtcpy(Fmt *f, const void *vm, int n, int sz);
void* __fmtdispatch(Fmt *f, void *fmt, int isrunes);
void * __fmtflush(Fmt *f, void *t, int len);
-void __fmtlock(void);
int __fmtpad(Fmt *f, int n);
double __fmtpow10(int n);
int __fmtrcpy(Fmt *f, const void *vm, int n);
-void __fmtunlock(void);
+void __fmtrlock(void);
+void __fmtrunlock(void);
+void __fmtwlock(void);
+void __fmtwunlock(void);
int __ifmt(Fmt *f);
int __isInf(double d, int sign);
int __isNaN(double d);
DIR diff --git a/src/lib9/fmt/fmtlock.c b/src/lib9/fmt/fmtlock.c
t@@ -5,11 +5,21 @@
#include "fmtdef.h"
void
-__fmtlock(void)
+__fmtrlock(void)
{
}
void
-__fmtunlock(void)
+__fmtrunlock(void)
+{
+}
+
+void
+__fmtwlock(void)
+{
+}
+
+void
+__fmtwunlock(void)
{
}
DIR diff --git a/src/lib9/fmtlock2.c b/src/lib9/fmtlock2.c
t@@ -1,16 +1,28 @@
#include <u.h>
#include <libc.h>
-static Lock fmtlock;
+static RWLock fmtlock;
void
-__fmtlock(void)
+__fmtrlock(void)
{
- lock(&fmtlock);
+ rlock(&fmtlock);
}
void
-__fmtunlock(void)
+__fmtrunlock(void)
{
- unlock(&fmtlock);
+ runlock(&fmtlock);
+}
+
+void
+__fmtwlock(void)
+{
+ wlock(&fmtlock);
+}
+
+void
+__fmtwunlock(void)
+{
+ wunlock(&fmtlock);
}