The smp_processor_id() shouldn't be called from preemptible code.
Instead use get_cpu() and put_cpu() which disables preemption in
addition to getting the processor id. Enable preemption back after
calling schedule_work() to make sure that the work gets scheduled on all
cores other than the current core. We want to avoid a scenario where
current core's stack trace is printed multiple times and one core's
stack trace isn't printed because of scheduling of current task.
This fixes the following bug:
[ 119.143590] sysrq: Show backtrace of all active CPUs
[ 119.143902] BUG: using smp_processor_id() in preemptible [00000000] code: bash/873
[ 119.144586] caller is debug_smp_processor_id+0x20/0x30
[ 119.144827] CPU: 6 PID: 873 Comm: bash Not tainted 5.10.124-dirty #3
[ 119.144861] Hardware name: QEMU QEMU Virtual Machine, BIOS 2023.05-1 07/22/2023
[ 119.145053] Call trace:
[ 119.145093] dump_backtrace+0x0/0x1a0
[ 119.145122] show_stack+0x18/0x70
[ 119.145141] dump_stack+0xc4/0x11c
[ 119.145159] check_preemption_disabled+0x100/0x110
[ 119.145175] debug_smp_processor_id+0x20/0x30
[ 119.145195] sysrq_handle_showallcpus+0x20/0xc0
[ 119.145211] __handle_sysrq+0x8c/0x1a0
[ 119.145227] write_sysrq_trigger+0x94/0x12c
[ 119.145247] proc_reg_write+0xa8/0xe4
[ 119.145266] vfs_write+0xec/0x280
[ 119.145282] ksys_write+0x6c/0x100
[ 119.145298] __arm64_sys_write+0x20/0x30
[ 119.145315] el0_svc_common.constprop.0+0x78/0x1e4
[ 119.145332] do_el0_svc+0x24/0x8c
[ 119.145348] el0_svc+0x10/0x20
[ 119.145364] el0_sync_handler+0x134/0x140
[ 119.145381] el0_sync+0x180/0x1c0
Cc: jirislaby@xxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
---
Changes since v3:
- Update commit message to explain why preemption reenabling must happen
after calling schedule_work()
Changes since v2:
- Add changelog and resend
Changes since v1:
- Add "Cc: stable@xxxxxxxxxxxxxxx" tag
---
drivers/tty/sysrq.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 23198e3f1461a..6b4a28bcf2f5f 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -262,13 +262,14 @@ static void sysrq_handle_showallcpus(u8 key)
if (in_hardirq())
regs = get_irq_regs();
- pr_info("CPU%d:\n", smp_processor_id());
+ pr_info("CPU%d:\n", get_cpu());
if (regs)
show_regs(regs);
else
show_stack(NULL, NULL, KERN_INFO);
schedule_work(&sysrq_showallcpus);
+ put_cpu();
}
}
--
2.40.1
