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Subject[PATCH] {double,triple}_down() in fs.h
Date
This time I've read SubmittingPatches and tried to follow the rules,
especially the one saying that a patch shouldn't be sent as an attachment.

The code of triple_down() looked ugly and complicated, but I found that it
just sorted the semaphores and down()ed them. So I rewrote the code making
it simpler and more efficient.

The patch was made w.r.t 2.4.14.

Per Persson
per.persson@gnosjo.pp.se


--- include/linux/fs.h.orig Mon Nov 12 01:14:10 2001
+++ include/linux/fs.h Tue Nov 13 17:35:16 2001
@@ -1478,14 +1478,25 @@
/*
* Whee.. Deadlock country. Happily there are only two VFS
* operations that does this..
+ *
+ * {double,triple}_down modified by Per Persson in September, 2001
*/
+
+#define exch(x,y) \
+do { \
+ typeof(x) __tmp__ = (x); \
+ (x) = (y); \
+ (y) = __tmp__; \
+} while(0)
+
+#define sort(x,y) \
+if((x) < (y)) \
+ exch((x), (y))
+
static inline void double_down(struct semaphore *s1, struct semaphore *s2)
{
- if (s1 != s2) {
- if ((unsigned long) s1 < (unsigned long) s2) {
- struct semaphore *tmp = s2;
- s2 = s1; s1 = tmp;
- }
+ if (s1 != s2)
+ sort((ulong)s1, (ulong)s2); // s1 > s2
down(s1);
}
down(s2);
@@ -1495,9 +1506,10 @@
* Ewwwwwwww... _triple_ lock. We are guaranteed that the 3rd argument is
* not equal to 1st and not equal to 2nd - the first case (target is parent
of
* source) would be already caught, the second is plain impossible (target
is
- * its own parent and that case would be caught even earlier). Very messy.
- * I _think_ that it works, but no warranties - please, look it through.
- * Pox on bloody lusers who mandated overwriting rename() for
directories...
+ * its own parent and that case would be caught even earlier).
+ *
+ * Cleaner and more efficient code than the original.
+ * /Per
*/

static inline void triple_down(struct semaphore *s1,
@@ -1505,33 +1517,17 @@
struct semaphore *s3)
{
if (s1 != s2) {
- if ((unsigned long) s1 < (unsigned long) s2) {
- if ((unsigned long) s1 < (unsigned long) s3) {
- struct semaphore *tmp = s3;
- s3 = s1; s1 = tmp;
- }
- if ((unsigned long) s1 < (unsigned long) s2) {
- struct semaphore *tmp = s2;
- s2 = s1; s1 = tmp;
- }
- } else {
- if ((unsigned long) s1 < (unsigned long) s3) {
- struct semaphore *tmp = s3;
- s3 = s1; s1 = tmp;
- }
- if ((unsigned long) s2 < (unsigned long) s3) {
- struct semaphore *tmp = s3;
- s3 = s2; s2 = tmp;
- }
- }
+ sort((ulong)s1, (ulong)s2); // s1 > s2
+ sort((ulong)s1, (ulong)s3); // s1 > s3
down(s1);
- } else if ((unsigned long) s2 < (unsigned long) s3) {
- struct semaphore *tmp = s3;
- s3 = s2; s2 = tmp;
}
+ sort((ulong)s2, (ulong)s3); // s2 > s3
down(s2);
down(s3);
}
+
+#undef sort
+#undef exch

static inline void double_up(struct semaphore *s1, struct semaphore *s2)
{
-
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