[PATCH] x86/fpu: drop_fpu() should not assume that tsk == current

Oleg Nesterov
2015-03-09T17:16:39Z

drop_fpu() does clear_used_math() and usually this is correct because
tsk == current. However switch_fpu_finish()->restore_fpu_checking() is
called before it updates the "current_task" variable. If it fails, we
will wrongly clear the PF_USED_MATH flag of the previous task.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
---
arch/x86/include/asm/fpu-internal.h | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 99a2067..81c86fa 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -336,7 +336,7 @@ static inline void drop_fpu(struct task_struct *tsk)
preempt_disable();
tsk->thread.fpu_counter = 0;
__drop_fpu(tsk);
- clear_used_math();
+ clear_stopped_child_used_math(tsk);
preempt_enable();
}

--
1.5.5.1