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Subject[PATCH 17/33] x86/fpu: Split the state handling in fpu__drop()
Date
Prepare fpu__drop() to use fpu->fpregs_active.

There are two distinct usecases for fpu__drop() in this context:
exit_thread() when called for 'current' in exit(), and when called
for another task in fork().

This patch does not change behavior, it only adds a couple of
debug checks and structures the code to make the ->fpregs_active
change more obviously correct.

All the complications will be removed later on.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/fpu/core.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index b7dc3833d41a..815dfba7781a 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -414,12 +414,19 @@ void fpu__drop(struct fpu *fpu)
{
preempt_disable();

- if (fpu->fpregs_active) {
- /* Ignore delayed exceptions from user space */
- asm volatile("1: fwait\n"
- "2:\n"
- _ASM_EXTABLE(1b, 2b));
- fpregs_deactivate(fpu);
+ if (fpu == &current->thread.fpu) {
+ WARN_ON_FPU(fpu->fpstate_active != fpu->fpregs_active);
+
+ if (fpu->fpregs_active) {
+ /* Ignore delayed exceptions from user space */
+ asm volatile("1: fwait\n"
+ "2:\n"
+ _ASM_EXTABLE(1b, 2b));
+ if (fpu->fpregs_active)
+ fpregs_deactivate(fpu);
+ }
+ } else {
+ WARN_ON_FPU(fpu->fpregs_active);
}

fpu->fpstate_active = 0;
--
2.11.0
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