Messages in this thread Patch in this message |  | | From | riel@redhat ... | Subject | [PATCH 2/8] x86, fpu: unlazy_fpu: don't do __thread_fpu_end() if use_eager_fpu() | Date | Fri, 6 Feb 2015 15:01:59 -0500 |
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From: Oleg Nesterov <oleg@redhat.com>
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: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Rik van Riel <riel@redhat.com> --- arch/x86/kernel/i387.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index c3b92c0975cd..8e070a6c30e5 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -120,8 +120,12 @@ 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(); } -- 1.9.3
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