[PATCH v10 11/12] arm64: factor work_pending state machine to C
From: Will Deacon <hidden>
Date: 2016-03-04 16:38:17
Also in:
lkml
Hi Chris, On Wed, Mar 02, 2016 at 03:09:35PM -0500, Chris Metcalf 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 closely mirror the existing behaviour while using
the usual C control flow primitives. As local_irq_{disable,enable} may
be instrumented, we balance exception entry (where we will almost most
likely enable IRQs) with a call to trace_hardirqs_on just before the
return to userspace.[...]
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 1f7f5a2b61bf..966d0d4308f2 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S@@ -674,18 +674,13 @@ ret_fast_syscall_trace: * 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: #ifdef CONFIG_TRACE_IRQFLAGS - bl trace_hardirqs_off // the IRQs are off here, inform the tracing code + bl trace_hardirqs_on // enabled while in userspace
This doesn't look right to me. We only get here after running do_notify_resume, which returns with interrupts disabled. Do we not instead need to inform the tracing code that interrupts are disabled prior to calling do_notify_resume?
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index e18c48cb6db1..3432e14b7d6e 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c@@ -402,15 +402,29 @@ static void do_signal(struct pt_regs *regs) asmlinkage void do_notify_resume(struct pt_regs *regs, unsigned int thread_flags) { - if (thread_flags & _TIF_SIGPENDING) - do_signal(regs); + while (true) { - if (thread_flags & _TIF_NOTIFY_RESUME) { - clear_thread_flag(TIF_NOTIFY_RESUME); - tracehook_notify_resume(regs); - } + if (thread_flags & _TIF_NEED_RESCHED) { + schedule(); + } else { + local_irq_enable(); + + if (thread_flags & _TIF_SIGPENDING) + do_signal(regs); - if (thread_flags & _TIF_FOREIGN_FPSTATE) - fpsimd_restore_current_state(); + 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(); + } + local_irq_disable(); + + thread_flags = READ_ONCE(current_thread_info()->flags); + if (!(thread_flags & _TIF_WORK_MASK)) + break; + }
This might be easier to read as a do { ... } while.
Will