(CC correctly linux-rt-users)
On 04/03/2019 17:20, Julien Grall wrote:
At the moment show_lock is implemented using spin_lock_t and called from
an interrupt context on Arm64. The following backtrace was triggered by:
42sh# echo l > /proc/sysrq-trigger
[ 4432.073756] sysrq: SysRq : Show backtrace of all active CPUs
[ 4432.403422] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:974
[ 4432.403424] sysrq: CPU6:
[ 4432.403426] in_atomic(): 1, irqs_disabled(): 128, pid: 2410, name: kworker/u16:2
[...]
[ 4432.403581] Call trace:
[ 4432.403584] dump_backtrace+0x0/0x148
[ 4432.403586] show_stack+0x14/0x20
[ 4432.403588] dump_stack+0x9c/0xd4
[ 4432.403592] ___might_sleep+0x1cc/0x298
[ 4432.403595] rt_spin_lock+0x5c/0x70
[ 4432.403596] showacpu+0x34/0x68
[ 4432.403599] flush_smp_call_function_queue+0xd4/0x278
[ 4432.403602] generic_smp_call_function_single_interrupt+0x10/0x18
[ 4432.403605] handle_IPI+0x26c/0x668
[ 4432.403607] gic_handle_irq+0x9c/0xa0
[ 4432.403609] el1_irq+0xb4/0x13c
With RT-patches, spin_lock can now sleep and therefore cannot be used from
interrupt context. Use a raw_spin_lock instead to prevent the lock to
sleep.
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
drivers/tty/sysrq.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 1f03078ec352..8473557c7ab2 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -208,7 +208,7 @@ static struct sysrq_key_op sysrq_showlocks_op = {
#endif
#ifdef CONFIG_SMP
-static DEFINE_SPINLOCK(show_lock);
+static DEFINE_RAW_SPINLOCK(show_lock);
static void showacpu(void *dummy)
{
@@ -218,10 +218,10 @@ static void showacpu(void *dummy)
if (idle_cpu(smp_processor_id()))
return;
- spin_lock_irqsave(&show_lock, flags);
+ raw_spin_lock_irqsave(&show_lock, flags);
pr_info("CPU%d:\n", smp_processor_id());
show_stack(NULL, NULL);
- spin_unlock_irqrestore(&show_lock, flags);
+ raw_spin_unlock_irqrestore(&show_lock, flags);
}
static void sysrq_showregs_othercpus(struct work_struct *dummy)
--
Julien Grall
