[PATCH v2 3/5] x86, fpu: irq_fpu_usable: always return true if use_eager_fpu()

[Oleg Nesterov]

According to the comment and the changelog in 5187b28f "x86: Allow FPU
to be used at interrupt time even with eagerfpu", the __thread_has_fpu()
check was added to avoid the nested kernel_fpu_begin(). Now that we have
in_kernel_fpu we can remove this check and always return true.

__thread_has_fpu() can be false even if use_eager_fpu(), but this case
doesn't differ from !use_eager_fpu() case except we should not worry
about X86_CR0_TS, __kernel_fpu_begin/end will not touch this bit. And I
still think that "use_eager_fpu && (!__thread_has_fpu || !used_math)"
special cases should die, but this is off-topic right now.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 arch/x86/kernel/i387.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 19dd36d..7bc8236 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -30,8 +30,8 @@ static DEFINE_PER_CPU(bool, in_kernel_fpu);
  * be set (so that the clts/stts pair does nothing that is
  * visible in the interrupted kernel thread).
  *
- * Except for the eagerfpu case when we return 1 unless we've already
- * been eager and saved the state in kernel_fpu_begin().
+ * Except for the eagerfpu case when we return true; in the likely case
+ * the thread has FPU but we are not going to set/clear TS.
  */
 static inline bool interrupted_kernel_fpu_idle(void)
 {
@@ -39,7 +39,7 @@ static inline bool interrupted_kernel_fpu_idle(void)
 		return false;
 
 	if (use_eager_fpu())
-		return __thread_has_fpu(current);
+		return true;
 
 	return !__thread_has_fpu(current) &&
 		(read_cr0() & X86_CR0_TS);
-- 
1.5.5.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/