This is a note to let you know that I've just added the patch titled
tty/sysrq: replace smp_processor_id() with get_cpu()
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tty-sysrq-replace-smp_processor_id-with-get_cpu.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From dd976a97d15b47656991e185a94ef42a0fa5cfd4 Mon Sep 17 00:00:00 2001
From: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Date: Mon, 9 Oct 2023 21:20:20 +0500
Subject: tty/sysrq: replace smp_processor_id() with get_cpu()
From: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
commit dd976a97d15b47656991e185a94ef42a0fa5cfd4 upstream.
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>
Link: https://lore.kernel.org/r/20231009162021.3607632-1-usama.anjum@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/sysrq.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -263,13 +263,14 @@ static void sysrq_handle_showallcpus(int
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();
}
}
Patches currently in stable-queue which might be from usama.anjum@xxxxxxxxxxxxx are
queue-6.5/tty-sysrq-replace-smp_processor_id-with-get_cpu.patch
