[PATCH] triple_down in fs.h

Per Persson (per.persson@gnosjo.pp.se)
Thu, 18 Oct 2001 15:10:34 +0200


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First, I'd like to send a thank to the Linux community from my father who
passed away this morning. He was very impressed by Linux and other free or
semi-free software like Samba, MySQL, GIMP and StarOffice.

Now to the patch:
I've made a couple of minor (but important?) changes in my patch of
{double,triple}_down in include/linux/fs.h.

Changes:

1) Added #undef's of my macros.
Thanks to Mitchell Blank Jr who proposed this change.
Also thanks to Yaroslav Popovitch who told me he had got an error caused
by the lack of #undef's.

2) Changed the names of the macros to further minimize the risk for name
collision; exch -> exch_vars, sort -> sort_vars.

Per Persson
per.persson@gnosjo.pp.se

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--- include/linux/fs.h.orig Sat Sep 29 22:10:21 2001=0A=
+++ include/linux/fs.h Mon Oct 8 13:03:24 2001=0A=
@@ -1476,14 +1476,27 @@=0A=
/*=0A=
* Whee.. Deadlock country. Happily there are only two VFS=0A=
* operations that does this..=0A=
+ *=0A=
+ * {double,triple}_down modified by Per Persson in September, 2001=0A=
*/=0A=
+=0A=
+#define exch_vars(x,y) \=0A=
+do { \=0A=
+ typeof(x) __tmp__ =3D (x); \=0A=
+ (x) =3D (y); \=0A=
+ (y) =3D __tmp__; \=0A=
+ \=0A=
+ (void)(&(x) =3D=3D &(y)) /* typecheck */ \=0A=
+} while(0)=0A=
+=0A=
+#define sort_vars(x,y) \=0A=
+if((x) > (y)) \=0A=
+ exch_vars((x), (y))=0A=
+=0A=
static inline void double_down(struct semaphore *s1, struct semaphore =
*s2)=0A=
{=0A=
if (s1 !=3D s2) {=0A=
- if ((unsigned long) s1 < (unsigned long) s2) {=0A=
- struct semaphore *tmp =3D s2;=0A=
- s2 =3D s1; s1 =3D tmp;=0A=
- }=0A=
+ sort_vars((ulong) s2, (ulong) s1); // s2 < s1=0A=
down(s1);=0A=
}=0A=
down(s2);=0A=
@@ -1493,9 +1506,11 @@=0A=
* Ewwwwwwww... _triple_ lock. We are guaranteed that the 3rd argument =
is=0A=
* not equal to 1st and not equal to 2nd - the first case (target is =
parent of=0A=
* source) would be already caught, the second is plain impossible =
(target is=0A=
- * its own parent and that case would be caught even earlier). Very =
messy.=0A=
- * I _think_ that it works, but no warranties - please, look it through.=0A=
- * Pox on bloody lusers who mandated overwriting rename() for =
directories...=0A=
+ * its own parent and that case would be caught even earlier).=0A=
+ *=0A=
+ * Hopefully it does the same thing as the old code,=0A=
+ * but in a cleaner and more efficient way.=0A=
+ * /Per=0A=
*/=0A=
=0A=
static inline void triple_down(struct semaphore *s1,=0A=
@@ -1503,33 +1518,17 @@=0A=
struct semaphore *s3)=0A=
{=0A=
if (s1 !=3D s2) {=0A=
- if ((unsigned long) s1 < (unsigned long) s2) {=0A=
- if ((unsigned long) s1 < (unsigned long) s3) {=0A=
- struct semaphore *tmp =3D s3;=0A=
- s3 =3D s1; s1 =3D tmp;=0A=
- }=0A=
- if ((unsigned long) s1 < (unsigned long) s2) {=0A=
- struct semaphore *tmp =3D s2;=0A=
- s2 =3D s1; s1 =3D tmp;=0A=
- }=0A=
- } else {=0A=
- if ((unsigned long) s1 < (unsigned long) s3) {=0A=
- struct semaphore *tmp =3D s3;=0A=
- s3 =3D s1; s1 =3D tmp;=0A=
- }=0A=
- if ((unsigned long) s2 < (unsigned long) s3) {=0A=
- struct semaphore *tmp =3D s3;=0A=
- s3 =3D s2; s2 =3D tmp;=0A=
- }=0A=
- }=0A=
+ sort_vars((ulong) s2, (ulong) s1); // s2 < s1=0A=
+ sort_vars((ulong) s3, (ulong) s1); // s3 < s1=0A=
down(s1);=0A=
- } else if ((unsigned long) s2 < (unsigned long) s3) {=0A=
- struct semaphore *tmp =3D s3;=0A=
- s3 =3D s2; s2 =3D tmp;=0A=
}=0A=
+ sort_vars((ulong) s3, (ulong) s2); // s2 > s3=0A=
down(s2);=0A=
down(s3);=0A=
}=0A=
+=0A=
+#undef exch_vars=0A=
+#undef sort_vars=0A=
=0A=
static inline void double_up(struct semaphore *s1, struct semaphore *s2)=0A=
{=0A=

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