On Tue, Aug 22, 2023 at 02:01:11PM +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>
> ---
> Changes since v1:
> - Add "Cc: stable@xxxxxxxxxxxxxxx" tag
> ---
This is not a resend, it is a new version, v3. Otherwise I would be
confused with the original v2 which is different than this one...
thanks,
greg k-h
