Messages in this thread Patch in this message | | | Date | Wed, 6 Jan 2016 13:43:14 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH 2/2] arm64: factor work_pending state machine to C |
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On Tue, Jan 05, 2016 at 05:33:35PM +0000, Mark Rutland wrote: > 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.
I realised there is a problem with this for kernel built with TRACE_IRQFLAGS, as local_irq_{enable,disable}() will verify that the IRQ state is as expected.
In ret_fast_syscall we disable irqs behind the back of the tracer, so when we get into do_notify_resume we'll get a splat.
In the non-syscall cases we do not disable interrupts first, so we can't balance things in do_notify_resume.
We can either add a trace_hardirqs_off call to ret_fast_syscall, or we can use raw_local_irq_{disable,enable}. The latter would match the current behaviour (and is a nicer diff). Once the syscall path is moved to C it would be possible to use the non-raw variants all-over.
Catalin, are you happy with using the raw accessors in do_notify_resume, or would you prefer using trace_hardirqs_off?
Thanks, Mark.
> 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();
This should be raw_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();
... likewise, raw_local_irq_enable() here.
> > + 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 >
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