From: Oleg Nesterov <[email protected]> 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 <[email protected]> Signed-off-by: Rik van Riel <[email protected]> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
