Re: [PATCH] RISC-V: Fix unannoted hardirqs-on in return to userspace slow-path

Conor Dooley
2022-11-12T23:53:14Z

On Fri, Nov 11, 2022 at 05:31:08PM -0500, Andrew Bresticker wrote:
> The return to userspace path in entry.S may enable interrupts without the
> corresponding lockdep annotation, producing a splat[0] when DEBUG_LOCKDEP
> is enabled. Simply calling __trace_hardirqs_on() here gets a bit messy
> due to the use of RA to point back to ret_from_exception, so just move
> the whole slow-path loop into C. It's more readable and it lets us use
> local_irq_{enable,disable}(), avoiding the need for manual annotations
> altogether.
>
> [0]:
> ------------[ cut here ]------------
> DEBUG_LOCKS_WARN_ON(!lockdep_hardirqs_enabled())
> WARNING: CPU: 2 PID: 1 at kernel/locking/lockdep.c:5512 check_flags+0x10a/0x1e0
> Modules linked in:
> CPU: 2 PID: 1 Comm: init Not tainted 6.1.0-rc4-00160-gb56b6e2b4f31 #53
> Hardware name: riscv-virtio,qemu (DT)
> epc : check_flags+0x10a/0x1e0
> ra : check_flags+0x10a/0x1e0
> <snip>
> status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
> [<ffffffff808edb90>] lock_is_held_type+0x78/0x14e
> [<ffffffff8003dae2>] __might_resched+0x26/0x22c
> [<ffffffff8003dd24>] __might_sleep+0x3c/0x66
> [<ffffffff80022c60>] get_signal+0x9e/0xa70
> [<ffffffff800054a2>] do_notify_resume+0x6e/0x422
> [<ffffffff80003c68>] ret_from_exception+0x0/0x10
> irq event stamp: 44512
> hardirqs last enabled at (44511): [<ffffffff808f901c>] _raw_spin_unlock_irqrestore+0x54/0x62
> hardirqs last disabled at (44512): [<ffffffff80008200>] __trace_hardirqs_off+0xc/0x14
> softirqs last enabled at (44472): [<ffffffff808f9fbe>] __do_softirq+0x3de/0x51e
> softirqs last disabled at (44467): [<ffffffff80017760>] irq_exit+0xd6/0x104
> ---[ end trace 0000000000000000 ]---
> possible reason: unannotated irqs-on.
>
> Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
> ---
> This should also theoretically be fixed by the conversion to generic entry,
> but it's not clear how far away that series is from landing.

Heh.. In case this makes the cut instead - what commit does this fix?

> ---
> arch/riscv/kernel/entry.S | 18 +++++-------------
> arch/riscv/kernel/signal.c | 34 +++++++++++++++++++++-------------
> 2 files changed, 26 insertions(+), 26 deletions(-)
>
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index b9eda3fcbd6d..58dfa8595e19 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -263,12 +263,11 @@ ret_from_exception:
> #endif
> bnez s0, resume_kernel
>
> -resume_userspace:
> /* Interrupts must be disabled here so flags are checked atomically */
> REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
> andi s1, s0, _TIF_WORK_MASK
> - bnez s1, work_pending
> -
> + bnez s1, resume_userspace_slow
> +resume_userspace:
> #ifdef CONFIG_CONTEXT_TRACKING_USER
> call user_enter_callable
> #endif
> @@ -368,19 +367,12 @@ resume_kernel:
> j restore_all
> #endif
>
> -work_pending:
> +resume_userspace_slow:
> /* Enter slow path for supplementary processing */
> - la ra, ret_from_exception
> - andi s1, s0, _TIF_NEED_RESCHED
> - bnez s1, work_resched
> -work_notifysig:
> - /* Handle pending signals and notify-resume requests */
> - csrs CSR_STATUS, SR_IE /* Enable interrupts for do_notify_resume() */
> move a0, sp /* pt_regs */
> move a1, s0 /* current_thread_info->flags */
> - tail do_notify_resume
> -work_resched:
> - tail schedule
> + call do_work_pending
> + j resume_userspace
>
> /* Slow paths for ptrace. */
> handle_syscall_trace_enter:
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index 5c591123c440..bfb2afa4135f 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -313,19 +313,27 @@ static void do_signal(struct pt_regs *regs)
> }
>
> /*
> - * notification of userspace execution resumption
> - * - triggered by the _TIF_WORK_MASK flags
> + * Handle any pending work on the resume-to-userspace path, as indicated by
> + * _TIF_WORK_MASK. Entered from assembly with IRQs off.
> */
> -asmlinkage __visible void do_notify_resume(struct pt_regs *regs,
> - unsigned long thread_info_flags)
> +asmlinkage __visible void do_work_pending(struct pt_regs *regs,
> + unsigned long thread_info_flags)
> {
> - if (thread_info_flags & _TIF_UPROBE)
> - uprobe_notify_resume(regs);
> -
> - /* Handle pending signal delivery */
> - if (thread_info_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
> - do_signal(regs);
> -
> - if (thread_info_flags & _TIF_NOTIFY_RESUME)
> - resume_user_mode_work(regs);
> + do {
> + if (thread_info_flags & _TIF_NEED_RESCHED) {
> + schedule();
> + } else {
> + local_irq_enable();
> + if (thread_info_flags & _TIF_UPROBE)
> + uprobe_notify_resume(regs);
> + /* Handle pending signal delivery */
> + if (thread_info_flags & (_TIF_SIGPENDING |
> + _TIF_NOTIFY_SIGNAL))
> + do_signal(regs);
> + if (thread_info_flags & _TIF_NOTIFY_RESUME)
> + resume_user_mode_work(regs);
> + }
> + local_irq_disable();
> + thread_info_flags = read_thread_flags();
> + } while (thread_info_flags & _TIF_WORK_MASK);
> }
> --
> 2.25.1