Re: [PATCH 1/2] powerpc/process: fix nested output in show_user_instructions()
Le 21/08/2018 à 08:27, Michael Ellerman a écrit :
Christophe Leroy writes:
When two processes crash at the same time, we sometimes encounter
nesting in the middle of a line:
I think "interleaved" is the right word, rather than "nesting".
They're actually (potentially) completely unrelated segfaults, that just
happen to occur at the same time.
And in fact any output that happens simultaneously will mess things up,
it doesn't have to be another segfault.
Ok, i reworded in v2.
[4.365317] init[1]: segfault (11) at 0 nip 0 lr 0 code 1
[4.370452] init[1]: code:
[4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code 1
in sh[1000+14000]
[4.386829]
[4.391542] init[1]: code:
[4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be0
7d3e4b78 3bbd0c20 3b60
[4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f83 419e0028 <8923>
2f89 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
Signed-off-by: Christophe Leroy
---
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;
I'm sure your math is right, but still an on-stack buffer with sprintf()
is a bit scary.
Can you try using seq_buf instead? It is safe against overflow.
eg, something like:
struct seq_buf s;
char buf[96];
seq_buf_init(, buf, sizeof(buf));
...
seq_buf_printf(, ...);
Ok, I did that in v2. In the meantime I reworked the loop to avoid this
uggly test against i % 8 and this duplication of the pr_info() of the
code line.
Christophe
Re: [PATCH 1/2] powerpc/process: fix nested output in show_user_instructions()
Christophe Leroy writes:
> When two processes crash at the same time, we sometimes encounter
> nesting in the middle of a line:
I think "interleaved" is the right word, rather than "nesting".
They're actually (potentially) completely unrelated segfaults, that just
happen to occur at the same time.
And in fact any output that happens simultaneously will mess things up,
it doesn't have to be another segfault.
> [4.365317] init[1]: segfault (11) at 0 nip 0 lr 0 code 1
> [4.370452] init[1]: code:
> [4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code
> 1 in sh[1000+14000]
> [4.386829]
> [4.391542] init[1]: code:
>
> [4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be0
> 7d3e4b78 3bbd0c20 3b60
> [4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f83 419e0028 <8923>
> 2f89 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
> Signed-off-by: Christophe Leroy
> ---
> 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;
I'm sure your math is right, but still an on-stack buffer with sprintf()
is a bit scary.
Can you try using seq_buf instead? It is safe against overflow.
eg, something like:
struct seq_buf s;
char buf[96];
seq_buf_init(, buf, sizeof(buf));
...
seq_buf_printf(, ...);
cheers
Re: [PATCH 1/2] powerpc/process: fix nested output in show_user_instructions()
Hi, Christophe.
On Tue, Aug 14, 2018 at 08:59:18AM +, Christophe Leroy wrote:
> 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:
> [4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code
> 1 in sh[1000+14000]
> [4.386829]
> [4.391542] init[1]: code:
>
> [4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be0
> 7d3e4b78 3bbd0c20 3b60
> [4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f83 419e0028 <8923>
> 2f89 41be001c 4b7f6e79
My smoke test passed with the two patches.
Perhaps adding an output sample of how messages would look like after your patch
could be an enhancement to the commit message.
Otherwise:
Reviewed-by: Murilo Opsfelder Araujo
> 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
> Signed-off-by: Christophe Leroy
> ---
> 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(" ");
> + l += sprintf(buf + l, " ");
> } 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
>
--
Murilo
[PATCH 1/2] powerpc/process: fix nested output in show_user_instructions()
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:
[4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code 1
in sh[1000+14000]
[4.386829]
[4.391542] init[1]: code:
[4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be0
7d3e4b78 3bbd0c20 3b60
[4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f83 419e0028 <8923>
2f89 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
Signed-off-by: Christophe Leroy
---
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(" ");
+ l += sprintf(buf + l, " ");
} 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
