x86: ignore the sys_getcpu() tcache parameter
dont use the vgetcpu tcache - it's causing problems with tasks
migrating, they'll see the old cache up to a jiffy after the
migration, further increasing the costs of the migration.
In the worst case they see a complete bogus information from
the tcache, when a sys_getcpu() call "invalidated" the cache
info by incrementing the jiffies _and_ the cpuid info in the
cache and the following vdso_getcpu() call happens after
vdso_jiffies have been incremented.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c
index 91f6e85..3b1ae1a 100644
--- a/arch/x86/vdso/vgetcpu.c
+++ b/arch/x86/vdso/vgetcpu.c
@@ -13,32 +13,17 @@
#include <asm/vgtod.h>
#include "vextern.h"
-long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
+long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
{
unsigned int dummy, p;
- unsigned long j = 0;
- /* Fast cache - only recompute value once per jiffies and avoid
- relatively costly rdtscp/cpuid otherwise.
- This works because the scheduler usually keeps the process
- on the same CPU and this syscall doesn't guarantee its
- results anyways.
- We do this here because otherwise user space would do it on
- its own in a likely inferior way (no access to jiffies).
- If you don't like it pass NULL. */
- if (tcache && tcache->blob[0] == (j = *vdso_jiffies)) {
- p = tcache->blob[1];
- } else if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
+ if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
rdtscp(dummy, dummy, p);
} else {
/* Load per CPU data from GDT */
asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
}
- if (tcache) {
- tcache->blob[0] = j;
- tcache->blob[1] = p;
- }
if (cpu)
*cpu = p & 0xfff;
if (node)