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

* [PATCH] riscv: Fixup boot failure when CONFIG_RT_MUTEXES=y
@ 2024-11-30 11:53 guoren
  2024-11-30 12:02 ` Guo Ren
  0 siblings, 1 reply; 3+ messages in thread
From: guoren @ 2024-11-30 11:53 UTC (permalink / raw)
  To: paul.walmsley, palmer, guoren, bjorn, conor, leobras, peterz,
	parri.andrea, will, longman, boqun.feng, arnd, alexghiti
  Cc: linux-riscv, linux-kernel, Guo Ren

From: Guo Ren <guoren@linux.alibaba.com>

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


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