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x86: ignore the sys_getcpu() tcache parameter

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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>
This commit is contained in:
Ingo Molnar
2007-11-07 18:37:48 +01:00
committed by Thomas Gleixner
parent 434b3d3209
commit 4307d1e5ad
2 changed files with 3 additions and 36 deletions
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20
kernel/sys.c
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@@ -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;
}