From dddd2bd98cb2a547c9fd08d68273c69d5bca3e1f Mon Sep 17 00:00:00 2001 From: Jibin Xu Date: Sun, 10 Sep 2017 20:11:42 -0700 Subject: [PATCH] sysrq : fix Show Regs call trace on ARM [ Upstream commit b00bebbc301c8e1f74f230dc82282e56b7e7a6db ] When kernel configuration SMP,PREEMPT and DEBUG_PREEMPT are enabled, echo 1 >/proc/sys/kernel/sysrq echo p >/proc/sysrq-trigger kernel will print call trace as below: sysrq: SysRq : Show Regs BUG: using __this_cpu_read() in preemptible [00000000] code: sh/435 caller is __this_cpu_preempt_check+0x18/0x20 Call trace: [] dump_backtrace+0x0/0x1d0 [] show_stack+0x24/0x30 [] dump_stack+0x90/0xb0 [] check_preemption_disabled+0x100/0x108 [] __this_cpu_preempt_check+0x18/0x20 [] sysrq_handle_showregs+0x1c/0x40 [] __handle_sysrq+0x12c/0x1a0 [] write_sysrq_trigger+0x60/0x70 [] proc_reg_write+0x90/0xd0 [] __vfs_write+0x48/0x90 [] vfs_write+0xa4/0x190 [] SyS_write+0x54/0xb0 [] el0_svc_naked+0x24/0x28 This can be seen on a common board like an r-pi3. This happens because when echo p >/proc/sysrq-trigger, get_irq_regs() is called outside of IRQ context, if preemption is enabled in this situation,kernel will print the call trace. Since many prior discussions on the mailing lists have made it clear that get_irq_regs either just returns NULL or stale data when used outside of IRQ context,we simply avoid calling it outside of IRQ context. Signed-off-by: Jibin Xu Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/tty/sysrq.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index d008f5a75197..377b3592384e 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -246,8 +246,10 @@ static void sysrq_handle_showallcpus(int key) * architecture has no support for it: */ if (!trigger_all_cpu_backtrace()) { - struct pt_regs *regs = get_irq_regs(); + struct pt_regs *regs = NULL; + if (in_irq()) + regs = get_irq_regs(); if (regs) { pr_info("CPU%d:\n", smp_processor_id()); show_regs(regs); @@ -266,7 +268,10 @@ static struct sysrq_key_op sysrq_showallcpus_op = { static void sysrq_handle_showregs(int key) { - struct pt_regs *regs = get_irq_regs(); + struct pt_regs *regs = NULL; + + if (in_irq()) + regs = get_irq_regs(); if (regs) show_regs(regs); perf_event_print_debug(); -- 2.20.1