Re: [PATCH v2] tty/sysrq: replace smp_processor_id() with get_cpu()

[Greg Kroah-Hartman]

On Tue, Aug 22, 2023 at 01:52:03PM +0500, Muhammad Usama Anjum wrote:
> 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. 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: stable@xxxxxxxxxxxxxxx
> Fixes: 47cab6a722d4 ("debug lockups: Improve lockup detection, fix generic arch fallback")
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> ---
>  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
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
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  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

If you wish to discuss this problem further, or you have questions about
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thanks,

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