On 11/25/2021 05:34 PM, Thomas Bogendoerfer wrote:
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")
Thank you, will add in v2.
---
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 ?
OK, no problem, using raw_cpu_has_fpu can also fix the issue and looks
better, I will send v2 soon.
Thanks,
Tiezhu
Thomas.
