[PATCH 2/2] arm64: factor work_pending state machine to C

Mark Rutland
2016-01-05T17:33:35Z

Currently ret_fast_syscall, work_pending, and ret_to_user form an ad-hoc
state machine that can be difficult to reason about due to duplicated
code and a large number of branch targets.

This patch factors the common logic out into the existing
do_notify_resume function, converting the code to C in the process,
making the code more legible.

This patch tries to mirror the existing behaviour as closely as possible
while using the usual C control flow primitives. There should be no
functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/entry.S | 24 +++---------------------
arch/arm64/kernel/signal.c | 36 ++++++++++++++++++++++++++----------
2 files changed, 29 insertions(+), 31 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 6b30ab1..41f5dfc 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -612,35 +612,17 @@ ret_fast_syscall:
ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing
and x2, x1, #_TIF_SYSCALL_WORK
cbnz x2, ret_fast_syscall_trace
- and x2, x1, #_TIF_WORK_MASK
- cbnz x2, work_pending
- enable_step_tsk x1, x2
- kernel_exit 0
+ b ret_to_user
ret_fast_syscall_trace:
enable_irq // enable interrupts
b __sys_trace_return_skipped // we already saved x0

/*
- * Ok, we need to do extra processing, enter the slow path.
- */
-work_pending:
- tbnz x1, #TIF_NEED_RESCHED, work_resched
- /* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
- mov x0, sp // 'regs'
- enable_irq // enable interrupts for do_notify_resume()
- bl do_notify_resume
- b ret_to_user
-work_resched:
- bl schedule
-
-/*
* "slow" syscall return path.
*/
ret_to_user:
- disable_irq // disable interrupts
- ldr x1, [tsk, #TI_FLAGS]
- and x2, x1, #_TIF_WORK_MASK
- cbnz x2, work_pending
+ bl do_notify_resume
+ ldr x1, [tsk, #TI_FLAGS] // re-check for single-step
enable_step_tsk x1, x2
kernel_exit 0
ENDPROC(ret_to_user)
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index e18c48c..3a6c60b 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -399,18 +399,34 @@ static void do_signal(struct pt_regs *regs)
restore_saved_sigmask();
}

-asmlinkage void do_notify_resume(struct pt_regs *regs,
- unsigned int thread_flags)
+asmlinkage void do_notify_resume(void)
{
- if (thread_flags & _TIF_SIGPENDING)
- do_signal(regs);
+ struct pt_regs *regs = task_pt_regs(current);
+ unsigned long thread_flags;

- if (thread_flags & _TIF_NOTIFY_RESUME) {
- clear_thread_flag(TIF_NOTIFY_RESUME);
- tracehook_notify_resume(regs);
- }
+ for (;;) {
+ local_irq_disable();
+
+ thread_flags = READ_ONCE(current_thread_info()->flags);
+ if (!(thread_flags & _TIF_WORK_MASK))
+ break;
+
+ if (thread_flags & _TIF_NEED_RESCHED) {
+ schedule();
+ continue;
+ }

- if (thread_flags & _TIF_FOREIGN_FPSTATE)
- fpsimd_restore_current_state();
+ local_irq_enable();

+ if (thread_flags & _TIF_SIGPENDING)
+ do_signal(regs);
+
+ if (thread_flags & _TIF_NOTIFY_RESUME) {
+ clear_thread_flag(TIF_NOTIFY_RESUME);
+ tracehook_notify_resume(regs);
+ }
+
+ if (thread_flags & _TIF_FOREIGN_FPSTATE)
+ fpsimd_restore_current_state();
+ }
}
--
1.9.1