On Fri, Sep 07, 2018 at 01:47:31PM +0000, Christophe Leroy wrote:
> When two processes crash at the same time, we sometimes encounter
> interleaving in the middle of a line:
>
> [ 4.365317] init[1]: segfault (11) at 0 nip 0 lr 0 code 1
> [ 4.370452] init[1]: code: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
> [ 4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code
> 1 in sh[10000000+14000]
> [ 4.386829] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
> [ 4.391542] init[1]: code: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
> XXXXXXXX XXXXXXXX XXXXXXXX
> [ 4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be00000
> 7d3e4b78 3bbd0c20 3b600000
> [ 4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f830000 419e0028 <89230000>
> 2f890000 41be001c 4b7f6e79
>
> This patch fixes it by preparing complete lines in a buffer and
> printing it at once.
>
> Fixes: 88b0fe1757359 ("powerpc: Add show_user_instructions()")
> Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
Reviewed-by: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
> ---
> v3: no change
> v2: Using seq_buf and reworked the loop to avoid redundant prints.
>
> arch/powerpc/kernel/process.c | 37 +++++++++++++++++++------------------
> 1 file changed, 19 insertions(+), 18 deletions(-)
>
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index e108e1ef2b85..2a39f7aca846 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -43,6 +43,7 @@
> #include <linux/uaccess.h>
> #include <linux/elf-randomize.h>
> #include <linux/pkeys.h>
> +#include <linux/seq_buf.h>
>
> #include <asm/pgtable.h>
> #include <asm/io.h>
> @@ -1303,33 +1304,33 @@ static void show_instructions(struct pt_regs *regs)
> void show_user_instructions(struct pt_regs *regs)
> {
> unsigned long pc;
> - int i;
> + int n = instructions_to_print;
> + struct seq_buf s;
> + char buf[96]; /* enough for 8 times 9 + 2 chars */
>
> pc = regs->nip - (instructions_to_print * 3 / 4 * sizeof(int));
>
> - pr_info("%s[%d]: code: ", current->comm, current->pid);
> + seq_buf_init(&s, buf, sizeof(buf));
>
> - for (i = 0; i < instructions_to_print; i++) {
> - int instr;
> + while (n) {
> + int i;
>
> - if (!(i % 8) && (i > 0)) {
> - pr_cont("\n");
> - pr_info("%s[%d]: code: ", current->comm, current->pid);
> - }
> + seq_buf_clear(&s);
>
> - if (probe_kernel_address((const void *)pc, instr)) {
> - pr_cont("XXXXXXXX ");
> - } else {
> - if (regs->nip == pc)
> - pr_cont("<%08x> ", instr);
> - else
> - pr_cont("%08x ", instr);
> + for (i = 0; i < 8 && n; i++, n--, pc += sizeof(int)) {
> + int instr;
> +
> + if (probe_kernel_address((const void *)pc, instr)) {
> + seq_buf_puts(&s, "XXXXXXXX ");
> + continue;
> + }
> + seq_buf_printf(&s, regs->nip == pc ? "<%08x> " : "%08x
> ", instr);
> }
>
> - pc += sizeof(int);
> + if (!seq_buf_has_overflowed(&s))
> + pr_info("%s[%d]: code: %s\n", current->comm,
> + current->pid, s.buffer);
> }
> -
> - pr_cont("\n");
> }
>
> struct regbit {
> --
> 2.13.3
>
--
Murilo
