From: Julien Grall Date: Wed, 13 Mar 2019 11:40:34 +0000 Subject: [PATCH 262/351] tty/sysrq: Convert show_lock to raw_spinlock_t Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=0fa8918b8835b046e47ce2bc5de45e815faebd80 Systems which don't provide arch_trigger_cpumask_backtrace() will invoke showacpu() from a smp_call_function() function which is invoked with disabled interrupts even on -RT systems. The function acquires the show_lock lock which only purpose is to ensure that the CPUs don't print simultaneously. Otherwise the output would clash and it would be hard to tell the output from CPUx apart from CPUy. On -RT the spin_lock() can not be acquired from this context. A raw_spin_lock() is required. It will introduce the system's latency by performing the sysrq request and other CPUs will block on the lock until the request is done. This is okay because the user asked for a backtrace of all active CPUs and under "normal circumstances in production" this path should not be triggered. Signed-off-by: Julien Grall Signed-off-by: Steven Rostedt (VMware) [bigeasy@linuxtronix.de: commit description] Signed-off-by: Sebastian Andrzej Siewior Acked-by: Sebastian Andrzej Siewior Signed-off-by: Greg Kroah-Hartman Cc: stable-rt@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior --- 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 cee0274806c5..f785ca55fb85 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -215,7 +215,7 @@ 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) { @@ -225,10 +225,10 @@ 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)