Hi, I found this little bug and here's a patch.
The reading of a timer is determined if 1. the hypervisor is not
currently updating it (where it sets the LSB of the version) or 2. the
kernel didn't finish reading it before the hypervisor updated it (the
kernel version doesn't match the hypervisor version).
But the current code doesn't test the above case. Instead, by using a
binary or instead of a logical one, it would only repeat if the
hypervisor was updating __and__ we read the version before it started
updating (or we read it before we started updating, but the hypervisor
finished updating between the first part of the or and the second check).
I'm not use to thunderbird so I'm sending both an attachment and an
inline cut and paste.
-- Steve
Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
diff -r 9632ececc8f4 linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c
--- a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Wed Aug 02 10:13:30
2006 +0100
+++ b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Wed Aug 02 22:54:09
2006 -0400
@@ -292,7 +292,7 @@ static void update_wallclock(void)
shadow_tv.tv_sec = s->wc_sec;
shadow_tv.tv_nsec = s->wc_nsec;
rmb();
- } while ((s->wc_version & 1) | (shadow_tv_version ^ s->wc_version));
+ } while ((s->wc_version & 1) || (shadow_tv_version ^ s->wc_version));
if (!independent_wallclock)
__update_wallclock(shadow_tv.tv_sec, shadow_tv.tv_nsec);
@@ -319,7 +319,7 @@ static void get_time_values_from_xen(voi
dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
dst->tsc_shift = src->tsc_shift;
rmb();
- } while ((src->version & 1) | (dst->version ^ src->version));
+ } while ((src->version & 1) || (dst->version ^ src->version));
dst->tsc_to_usec_mul = dst->tsc_to_nsec_mul / 1000;
}
diff -r 9632ececc8f4 linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c
--- a/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Wed Aug 02 10:13:30
2006 +0100
+++ b/linux-2.6-xen-sparse/arch/i386/kernel/time-xen.c Wed Aug 02 22:54:09
2006 -0400
@@ -292,7 +292,7 @@ static void update_wallclock(void)
shadow_tv.tv_sec = s->wc_sec;
shadow_tv.tv_nsec = s->wc_nsec;
rmb();
- } while ((s->wc_version & 1) | (shadow_tv_version ^ s->wc_version));
+ } while ((s->wc_version & 1) || (shadow_tv_version ^ s->wc_version));
if (!independent_wallclock)
__update_wallclock(shadow_tv.tv_sec, shadow_tv.tv_nsec);
@@ -319,7 +319,7 @@ static void get_time_values_from_xen(voi
dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
dst->tsc_shift = src->tsc_shift;
rmb();
- } while ((src->version & 1) | (dst->version ^ src->version));
+ } while ((src->version & 1) || (dst->version ^ src->version));
dst->tsc_to_usec_mul = dst->tsc_to_nsec_mul / 1000;
}
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