Re: [PATCH] kdb: use correct pointer when 'btc' calls 'btt'

[Daniel Thompson]

On Fri, Sep 14, 2018 at 12:35:44PM +0000, Christophe Leroy wrote:
> On a powerpc 8xx, 'btc' fails as follows:
> 
> Entering kdb (current=0x(ptrval), pid 282) due to Keyboard Entry
> kdb> btc
> btc: cpu status: Currently on cpu 0
> Available cpus: 0
> kdb_getarea: Bad address 0x0
> 
> when booting the kernel with 'debug_boot_weak_hash', it fails as well
> 
> Entering kdb (current=0xba99ad80, pid 284) due to Keyboard Entry
> kdb> btc
> btc: cpu status: Currently on cpu 0
> Available cpus: 0
> kdb_getarea: Bad address 0xba99ad80
> 
> On other platforms, Oopses have been observed too, see
> https://github.com/linuxppc/linux/issues/139
> 
> This is due to btc calling 'btt' with %p pointer as an argument.
> 
> This patch replaces %p by %px to get the real pointer value as
> expected by 'btt'
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.15+

Would a Fixes: be better here?
Fixes: ad67b74d2469d9b82 ("printk: hash addresses printed with %p")

No blame attached to Tobin, but the fixes makes it super clear what
changed and why this breaks kdb (which was not explicitly called out
the patch description).


Daniel.

> ---
>  kernel/debug/kdb/kdb_bt.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_bt.c b/kernel/debug/kdb/kdb_bt.c
> index 6ad4a9fcbd6f..7921ae4fca8d 100644
> --- a/kernel/debug/kdb/kdb_bt.c
> +++ b/kernel/debug/kdb/kdb_bt.c
> @@ -179,14 +179,14 @@ kdb_bt(int argc, const char **argv)
>  				kdb_printf("no process for cpu %ld\n", cpu);
>  				return 0;
>  			}
> -			sprintf(buf, "btt 0x%p\n", KDB_TSK(cpu));
> +			sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
>  			kdb_parse(buf);
>  			return 0;
>  		}
>  		kdb_printf("btc: cpu status: ");
>  		kdb_parse("cpu\n");
>  		for_each_online_cpu(cpu) {
> -			sprintf(buf, "btt 0x%p\n", KDB_TSK(cpu));
> +			sprintf(buf, "btt 0x%px\n", KDB_TSK(cpu));
>  			kdb_parse(buf);
>  			touch_nmi_watchdog();
>  		}
> -- 
> 2.13.3
>