linux-kernel - Re: [PATCH] riscv: Fixup boot failure when CONFIG_RT

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Message-ID: <CAJF2gTQhfr-wsj2VZwwP7sWq=yp9HtT_kzzr68xh1VpKLSbybQ@mail.gmail.com>
Date: Sat, 30 Nov 2024 20:02:30 +0800
From: Guo Ren <guoren@...nel.org>
To: paul.walmsley@...ive.com, palmer@...belt.com, guoren@...nel.org, 
	bjorn@...osinc.com, conor@...nel.org, leobras@...hat.com, 
	peterz@...radead.org, parri.andrea@...il.com, will@...nel.org, 
	longman@...hat.com, boqun.feng@...il.com, arnd@...db.de, 
	alexghiti@...osinc.com
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH] riscv: Fixup boot failure when CONFIG_RT_MUTEXES=y

On Sat, Nov 30, 2024 at 7:54 PM <guoren@...nel.org> wrote:
>
> From: Guo Ren <guoren@...ux.alibaba.com>
>
> When CONFIG_RT_MUTEXES=y, mutex_lock->rt_mutex_try_acquire would
Correct: CONFIG_DEBUG_RT_MUTEXES=y

> change from rt_mutex_cmpxchg_acquire to rt_mutex_slowtrylock():
>         raw_spin_lock_irqsave(&lock->wait_lock, flags);
>         ret = __rt_mutex_slowtrylock(lock);
>         raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
>
> Because queued_spin_#ops to ticket_#ops is changed one by one by
> jump_label, raw_spin_lock/unlock would cause a deadlock during the
> changing.
>
> That means in arch/riscv/kernel/jump_label.c:
> 1.
> arch_jump_label_transform_queue() ->
> mutex_lock(&text_mutex); +-> raw_spin_lock  -> queued_spin_lock
>                          |-> raw_spin_unlock -> queued_spin_unlock
> patch_insn_write -> change the raw_spin_lock to ticket_lock
> mutex_unlock(&text_mutex);
> ...
>
> 2. /* Dirty the lock value */
> arch_jump_label_transform_queue() ->
> mutex_lock(&text_mutex); +-> raw_spin_lock -> *ticket_lock*
>                          |-> raw_spin_unlock -> *queued_spin_unlock*
>                           /* BUG: ticket_lock with queued_spin_unlock */
> patch_insn_write  ->  change the raw_spin_unlock to ticket_unlock
> mutex_unlock(&text_mutex);
> ...
>
> 3. /* Dead lock */
> arch_jump_label_transform_queue() ->
> mutex_lock(&text_mutex); +-> raw_spin_lock -> ticket_lock /* deadlock! */
>                          |-> raw_spin_unlock -> ticket_unlock
> patch_insn_write -> change other raw_spin_#op -> ticket_#op
> mutex_unlock(&text_mutex);
>
> So, the solution is to disable mutex usage of
> arch_jump_label_transform_queue() during early_boot_irqs_disabled, just
> like we have done for stop_machine.
>
> Reported-by: Conor Dooley <conor@...nel.org>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> Fixes: ab83647fadae ("riscv: Add qspinlock support")
> Link: https://lore.kernel.org/linux-riscv/CAJF2gTQwYTGinBmCSgVUoPv0_q4EPt_+WiyfUA1HViAKgUzxAg@mail.gmail.com/T/#mf488e6347817fca03bb93a7d34df33d8615b3775
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
>  arch/riscv/kernel/jump_label.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
> index 6eee6f736f68..654ed159c830 100644
> --- a/arch/riscv/kernel/jump_label.c
> +++ b/arch/riscv/kernel/jump_label.c
> @@ -36,9 +36,15 @@ bool arch_jump_label_transform_queue(struct jump_entry *entry,
>                 insn = RISCV_INSN_NOP;
>         }
>
> -       mutex_lock(&text_mutex);
> -       patch_insn_write(addr, &insn, sizeof(insn));
> -       mutex_unlock(&text_mutex);
> +       if (early_boot_irqs_disabled) {
> +               riscv_patch_in_stop_machine = 1;
> +               patch_insn_write(addr, &insn, sizeof(insn));
> +               riscv_patch_in_stop_machine = 0;
> +       } else {
> +               mutex_lock(&text_mutex);
> +               patch_insn_write(addr, &insn, sizeof(insn));
> +               mutex_unlock(&text_mutex);
> +       }
>
>         return true;
>  }
> --
> 2.40.1
>


-- 
Best Regards
 Guo Ren