[PATCH] riscv: Fixup boot failure when CONFIG_RT_MUTEXES=y

[Guo Ren]

On Sat, Nov 30, 2024 at 8:02 PM Guo Ren <guoren at kernel.org> wrote:
>
> On Sat, Nov 30, 2024 at 7:54 PM <guoren at kernel.org> wrote:
> >
> > From: Guo Ren <guoren at linux.alibaba.com>
> >
> > When CONFIG_RT_MUTEXES=y, mutex_lock->rt_mutex_try_acquire would
> Correct: CONFIG_DEBUG_RT_MUTEXES=y
Abandoned.

Here is the RESEND PATCH:
https://lore.kernel.org/linux-riscv/20241130153310.3349484-1-guoren@kernel.org/

>
> > 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 at kernel.org>
> > Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren at kernel.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 at dabbelt.com>
> > Cc: Alexandre Ghiti <alexghiti at rivosinc.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



-- 
Best Regards
 Guo Ren