Re: [PATCH] riscv: Fix sleeping in invalid context in die()

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2024-11-18 10:13:33 [+0100], Nam Cao wrote:
> die() can be called in exception handler, and therefore cannot sleep.
> However, die() takes spinlock_t which can sleep with PREEMPT_RT enabled.
> That causes the following warning:
> 
> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 285, name: mutex
> preempt_count: 110001, expected: 0
> RCU nest depth: 0, expected: 0
> CPU: 0 UID: 0 PID: 285 Comm: mutex Not tainted 6.12.0-rc7-00022-ge19049cf7d56-dirty #234
> Hardware name: riscv-virtio,qemu (DT)
> Call Trace:
>     dump_backtrace+0x1c/0x24
>     show_stack+0x2c/0x38
>     dump_stack_lvl+0x5a/0x72
>     dump_stack+0x14/0x1c
>     __might_resched+0x130/0x13a
>     rt_spin_lock+0x2a/0x5c
>     die+0x24/0x112
>     do_trap_insn_illegal+0xa0/0xea
>     _new_vmalloc_restore_context_a0+0xcc/0xd8
> Oops - illegal instruction [#1]
> 
> Switch to use raw_spinlock_t, which does not sleep even with PREEMPT_RT
> enabled.
> 
> Fixes: 76d2a0493a17 ("RISC-V: Init and Halt Code")
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> Cc: stable@vger.kernel.org

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

The die_lock() is probably do let one CPU die at a time. On x86 there is
support for for recursive die so if it happens, you don't spin on the
die_lock and see nothing. Not sure if this is a thing.

Sebastian