The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x dd976a97d15b47656991e185a94ef42a0fa5cfd4 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023112201-yiddish-limes-21d5@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^.. Possible dependencies: dd976a97d15b ("tty/sysrq: replace smp_processor_id() with get_cpu()") 5390e7f46b9d ("sysrq: do not omit current cpu when showing backtrace of all active CPUs") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >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: [PATCH] tty/sysrq: replace smp_processor_id() with get_cpu() 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> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 23198e3f1461..6b4a28bcf2f5 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(); } }
