Hi,
I experienced troubles when tracing a process with strace. Sometimes,
when I killed the strace process (SIGKILL), the traced process was also
killed. I found out that it was getting SIGTRAP and, indeed, when the
traced process set up a signal handler for SIGTRAP, it no longer died.
I noticed that normally, when the traced process is continued (via
PTRACE_CONT or similar), the signal to be sent to it is stored in
current->exit_code, which is then examined by the arch-specific code and
usually leads to something like:
send_sig(current->exit_code, current, 1);
The exit_code is set in ptrace_stop(), but the tracing process may go
away while the traced process waits for it, and in that case exit_code
is left as-is. I think we must set it to zero in ptrace_untrace().
Signed-off-by: Petr Tesarik <[email protected]>
ptrace.c | 1 +
1 file changed, 1 insertion(+)
diff -pru a/kernel/ptrace.c b/kernel/ptrace.c
--- a/kernel/ptrace.c 2007-12-04 14:12:51.000000000 +0100
+++ b/kernel/ptrace.c 2007-12-04 14:13:28.000000000 +0100
@@ -52,6 +52,7 @@ void ptrace_untrace(struct task_struct *
{
spin_lock(&child->sighand->siglock);
if (child->state == TASK_TRACED) {
+ child->exit_code = 0;
if (child->signal->flags & SIGNAL_STOP_STOPPED) {
child->state = TASK_STOPPED;
} else {
Petr Tesarik wrote:
> Hi,
>
> I experienced troubles when tracing a process with strace. Sometimes,
> when I killed the strace process (SIGKILL), the traced process was also
> killed. I found out that it was getting SIGTRAP and, indeed, when the
> traced process set up a signal handler for SIGTRAP, it no longer died.
>
> I noticed that normally, when the traced process is continued (via
> PTRACE_CONT or similar), the signal to be sent to it is stored in
> current->exit_code, which is then examined by the arch-specific code and
> usually leads to something like:
>
> send_sig(current->exit_code, current, 1);
>
> The exit_code is set in ptrace_stop(), but the tracing process may go
> away while the traced process waits for it, and in that case exit_code
> is left as-is. I think we must set it to zero in ptrace_untrace().
My patch was very wrong, but at least I produced a test case. It fails
on all systems I could test. The only correct solution (TM) could be
achieved if we could tell the tracee in ptrace_stop() that the tracer
actually died and it should use nostop_code instead of exit_code.
Possibly a new flag?
Regards,
Petr Tesarik