Re: [RESEND PATCH] riscv: Fixup boot failure when CONFIG_DEBUG_RT_MUTEXES=y

[Nam Cao]

On Sat, Nov 30, 2024 at 10:33:10AM -0500, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> 
> When CONFIG_DEBUG_RT_MUTEXES=y, mutex_lock->rt_mutex_try_acquire
> would 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@xxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> Fixes: ab83647fadae ("riscv: Add qspinlock support")
> Link: https://lore.kernel.org/linux-riscv/CAJF2gTQwYTGinBmCSgVUoPv0_q4EPt_+WiyfUA1HViAKgUzxAg@xxxxxxxxxxxxxx/T/#mf488e6347817fca03bb93a7d34df33d8615b3775
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>

Tested-by: Nam Cao <namcao@xxxxxxxxxxxxx>

Thanks for the fix,
Nam