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 (file)
--- 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)

diff --git a/kernel/sys.c b/kernel/sys.c
index 304b541..d1fe71e 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1750,7 +1750,7 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
 }
 
 asmlinkage long sys_getcpu(unsigned __user *cpup, unsigned __user *nodep,
-                          struct getcpu_cache __user *cache)
+                          struct getcpu_cache __user *unused)
 {
        int err = 0;
        int cpu = raw_smp_processor_id();
@@ -1758,24 +1758,6 @@ asmlinkage long sys_getcpu(unsigned __user *cpup, unsigned __user *nodep,
                err |= put_user(cpu, cpup);
        if (nodep)
                err |= put_user(cpu_to_node(cpu), nodep);
-       if (cache) {
-               /*
-                * The cache is not needed for this implementation,
-                * but make sure user programs pass something
-                * valid. vsyscall implementations can instead make
-                * good use of the cache. Only use t0 and t1 because
-                * these are available in both 32bit and 64bit ABI (no
-                * need for a compat_getcpu). 32bit has enough
-                * padding
-                */
-               unsigned long t0, t1;
-               get_user(t0, &cache->blob[0]);
-               get_user(t1, &cache->blob[1]);
-               t0++;
-               t1++;
-               put_user(t0, &cache->blob[0]);
-               put_user(t1, &cache->blob[1]);
-       }
        return err ? -EFAULT : 0;
 }