[5/9] arm64: correctly check for ktrheads

Message ID 20190814104131.20190-6-mark.rutland@arm.com
State New
Headers show
Series
  • kthread detection cleanup
Related show

Commit Message

Mark Rutland Aug. 14, 2019, 10:41 a.m.
Since commit:

  6eb6c80187c55b7f ("arm64: kernel thread don't need to save fpsimd context.")

... we skip saving the fpsimd state for kernel threads in
arch_dup_task_struct(). We determine whether current is a kthread by
looking at current->mm.

In general, a non-NULL current->mm doesn't imply that current is a
kthread, as kthreads can install an mm via use_mm(), and so it's
preferable to use is_kthread() to determine whether a thread is a
kthread.

For consistency, let's use is_kthread() here.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/process.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.11.0

Comments

Catalin Marinas Aug. 14, 2019, 4:40 p.m. | #1
On Wed, Aug 14, 2019 at 11:41:27AM +0100, Mark Rutland wrote:
> Since commit:

> 

>   6eb6c80187c55b7f ("arm64: kernel thread don't need to save fpsimd context.")

> 

> ... we skip saving the fpsimd state for kernel threads in

> arch_dup_task_struct(). We determine whether current is a kthread by

> looking at current->mm.

> 

> In general, a non-NULL current->mm doesn't imply that current is a

> kthread, as kthreads can install an mm via use_mm(), and so it's

> preferable to use is_kthread() to determine whether a thread is a

> kthread.

> 

> For consistency, let's use is_kthread() here.

> 

> Signed-off-by: Mark Rutland <mark.rutland@arm.com>

> Cc: Catalin Marinas <catalin.marinas@arm.com>

> Cc: Ingo Molnar <mingo@kernel.org>

> Cc: Peter Zijlstra <peterz@infradead.org>

> Cc: Will Deacon <will@kernel.org>


Acked-by: Catalin Marinas <catalin.marinas@arm.com>

Patch

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 288012687c29..82b0a7a257cd 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -335,7 +335,7 @@  void arch_release_task_struct(struct task_struct *tsk)
  */
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
-	if (current->mm)
+	if (!is_kthread(current))
 		fpsimd_preserve_current_state();
 	*dst = *src;