On Wed, 20 Nov 2024 00:50:45 PST (-0800), bigeasy@xxxxxxxxxxxxx wrote:
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@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxxReviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> 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.
Looks like the RISC-V code is pretty much the same as the arm64 code, so it probably just came from there. I don't really know what the right answer is here...
Sebastian
