[PATCH 1/2] powerpc/process: fix nested output in show_user_instructions()

From: Christophe Leroy
Date: Tue Aug 14 2018 - 09:27:38 EST


When two processes crash at the same time, we sometimes encounter
nesting 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 <muriloo@xxxxxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/kernel/process.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 913c5725cdb2..c722ce4ca1c0 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1303,32 +1303,33 @@ void show_user_instructions(struct pt_regs *regs)
{
unsigned long pc;
int i;
+ char buf[96]; /* enough for 8 times 9 + 2 chars */
+ int l = 0;

pc = regs->nip - (instructions_to_print * 3 / 4 * sizeof(int));

- pr_info("%s[%d]: code: ", current->comm, current->pid);
-
for (i = 0; i < instructions_to_print; i++) {
int instr;

if (!(i % 8) && (i > 0)) {
- pr_cont("\n");
- pr_info("%s[%d]: code: ", current->comm, current->pid);
+ pr_info("%s[%d]: code: %s\n", current->comm, current->pid, buf);
+ l = 0;
}

if (probe_kernel_address((unsigned int __user *)pc, instr)) {
- pr_cont("XXXXXXXX ");
+ l += sprintf(buf + l, "XXXXXXXX ");
} else {
if (regs->nip == pc)
- pr_cont("<%08x> ", instr);
+ l += sprintf(buf + l, "<%08x> ", instr);
else
- pr_cont("%08x ", instr);
+ l += sprintf(buf + l, "%08x ", instr);
}

pc += sizeof(int);
}

- pr_cont("\n");
+ if (l)
+ pr_info("%s[%d]: code: %s\n", current->comm, current->pid, buf);
}

struct regbit {
--
2.13.3