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/kernel/sys.c b/kernel/sys.c
index 304b541..d1fe71e 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1750,7 +1750,7 @@
}
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 @@
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;
}