Messages in this thread Patch in this message | | | Date | Mon, 19 Jan 2015 19:51:32 +0100 | From | Oleg Nesterov <> | Subject | [PATCH 1/3] x86, fpu: __kernel_fpu_begin() should clear fpu_owner_task even if use_eager_fpu() |
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__kernel_fpu_begin() does nothing if !__thread_has_fpu() && use_eager_fpu(), perhaps it assumes that this case is simply impossible. This is certainly not possible if in_interrupt() == T; interrupted_user_mode() should have FPU, and interrupted_kernel_fpu_idle() should fail if !__thread_has_fpu().
However, even if use_eager_fpu() == T a task can do drop_fpu(), then switch to another thread which becomes fpu_owner_task, then resume and call some function which does kernel_fpu_begin(). Say, an exiting task does a lot of things after exit_thread(), it is not safe to assume that it can't use FPU in these paths.
Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- arch/x86/kernel/i387.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index 81049ff..26f0e80 100644 --- a/arch/x86/kernel/i387.c +++ b/arch/x86/kernel/i387.c @@ -93,9 +93,10 @@ void __kernel_fpu_begin(void) if (__thread_has_fpu(me)) { __save_init_fpu(me); - } else if (!use_eager_fpu()) { + } else { this_cpu_write(fpu_owner_task, NULL); - clts(); + if (!use_eager_fpu()) + clts(); } } EXPORT_SYMBOL(__kernel_fpu_begin); -- 1.5.5.1
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