On Mon, Nov 22, 2021 at 06:17:37PM +0800, Tiezhu Yang wrote:
> There exists the following issue under DEBUG_PREEMPT:
>
> BUG: using smp_processor_id() in preemptible [00000000] code: systemd/1
> caller is show_cpuinfo+0x460/0xea0
> ...
> Call Trace:
> [<ffffffff8020f0dc>] show_stack+0x94/0x128
> [<ffffffff80e6cab4>] dump_stack_lvl+0x94/0xd8
> [<ffffffff80e74c5c>] check_preemption_disabled+0x104/0x110
> [<ffffffff802209c8>] show_cpuinfo+0x460/0xea0
> [<ffffffff80539d54>] seq_read_iter+0xfc/0x4f8
> [<ffffffff804fcc10>] new_sync_read+0x110/0x1b8
> [<ffffffff804ff57c>] vfs_read+0x1b4/0x1d0
> [<ffffffff804ffb18>] ksys_read+0xd0/0x110
> [<ffffffff8021c090>] syscall_common+0x34/0x58
>
> We can see the following call trace:
> show_cpuinfo()
> cpu_has_fpu
> current_cpu_data
> smp_processor_id()
>
> $ addr2line -f -e vmlinux 0xffffffff802209c8
> show_cpuinfo
> arch/mips/kernel/proc.c:188
>
> $ head -188 arch/mips/kernel/proc.c | tail -1
> if (cpu_has_fpu)
>
> arch/mips/include/asm/cpu-features.h
> # define cpu_has_fpu (current_cpu_data.options & MIPS_CPU_FPU)
>
> arch/mips/include/asm/cpu-info.h
> #define current_cpu_data cpu_data[smp_processor_id()]
>
> Based on the above analysis, fix the issue by disabling preemption
> around cpu_has_fpu in show_cpuinfo().
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
missing
Fixes: 626bfa037299 ("MIPS: kernel: proc: add CPU option reporting")
> ---
> arch/mips/kernel/proc.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/mips/kernel/proc.c b/arch/mips/kernel/proc.c
> index 376a6e2..c6c2661 100644
> --- a/arch/mips/kernel/proc.c
> +++ b/arch/mips/kernel/proc.c
> @@ -185,8 +185,10 @@ static int show_cpuinfo(struct seq_file *m, void *v)
> seq_puts(m, " tx39_cache");
> if (cpu_has_octeon_cache)
> seq_puts(m, " octeon_cache");
> + preempt_disable();
> if (cpu_has_fpu)
> seq_puts(m, " fpu");
> + preempt_enable();
what about using raw_cpu_has_fpu() instead ?
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
