提交 1a2a7f4e 编写于 作者: O Oleg Nesterov 提交者: Borislav Petkov

x86/fpu: Don't do __thread_fpu_end() if use_eager_fpu()

unlazy_fpu()->__thread_fpu_end() doesn't look right if use_eager_fpu().
Unconditional __thread_fpu_end() is only correct if we know that this
thread can't return to user-mode and use FPU.

Fortunately it has only 2 callers. fpu_copy() checks use_eager_fpu(),
and init_fpu(current) can be only called by the coredumping thread via
regset->get(). But it is exported to modules, and imo this should be
fixed anyway.

And if we check use_eager_fpu() we can use __save_fpu() like fpu_copy()
and save_init_fpu() do.

- It seems that even !use_eager_fpu() case doesn't need the unconditional
  __thread_fpu_end(), we only need it if __save_init_fpu() returns 0.

- It is still not clear to me if __save_init_fpu() can safely nest with
  another save + restore from __kernel_fpu_begin(). If not, we can use
  kernel_fpu_disable() to fix the race.
Signed-off-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NRik van Riel <riel@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1423252925-14451-3-git-send-email-riel@redhat.comSigned-off-by: NBorislav Petkov <bp@suse.de>
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......@@ -106,8 +106,12 @@ void unlazy_fpu(struct task_struct *tsk)
{
preempt_disable();
if (__thread_has_fpu(tsk)) {
__save_init_fpu(tsk);
__thread_fpu_end(tsk);
if (use_eager_fpu()) {
__save_fpu(tsk);
} else {
__save_init_fpu(tsk);
__thread_fpu_end(tsk);
}
}
preempt_enable();
}
......
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