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>

2 files changed, 3 insertions, 36 deletions

diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c
index 91f6e85d0fc2..3b1ae1abfba9 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)
diff --git a/kernel/sys.c b/kernel/sys.c
index 304b5410d746..d1fe71eb4546 100644
--- 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;
 }