powerpc: fork && stepping (Was: [RFC,PATCH 0/14] utrace/ptrace)

I changed the subject. This bug has nothing to do with utrace,
the kernel fails with or without these changes.

On 11/26, Ananth N Mavinakayanahalli wrote:

On Wed, Nov 25, 2009 at 04:40:52PM +0100, Oleg Nesterov wrote:
On 11/25, Ananth N Mavinakayanahalli wrote:

step-fork: step-fork.c:56: handler_fail: Assertion `0' failed.
/bin/sh: line 5: 24803 Aborted ${dir}$tst
FAIL: step-fork

This is expected. Should be fixed by

ptrace-copy_process-should-disable-stepping.patch

in -mm tree. (I am attaching this patch below just in case)
I din't mention this patch in this series because this bug
is "ortogonal" to utrace/ptrace.

The patch doesn't seem to fix the issue on powerpc:

step-fork: step-fork.c:56: handler_fail: Assertion `0' failed.
/bin/sh: line 5: 17325 Aborted ${dir}$tst
FAIL: step-fork

Good to know, thanks again Ananth.

I'll take a look. Since I know nothing about powerpc, I can't
promise the quick fix ;)

The bug was found by code inspection, but the fix is not trivial
because it depends on arch/, and it turns out the arch-independent
fix in

ptrace-copy_process-should-disable-stepping.patch
http://marc.info/?l=linux-mm-commits&m=125789789322573

doesn't work.

Ananth, could you please run the test-case from the changelog
below ? I do not really expect this can help, but just in case.

Oleg.

#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <assert.h>

int main(void)
{
int pid, status;

if (!(pid = fork())) {
assert(ptrace(PTRACE_TRACEME) == 0);
kill(getpid(), SIGSTOP);

if (!fork()) {
/* kernel bug: this child will be killed by SIGTRAP */
printf("Hello world\n");
return 43;
}

wait(&status);
return WEXITSTATUS(status);
}

for (;;) {
assert(pid == wait(&status));
if (WIFEXITED(status))
break;
assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0);
}

assert(WEXITSTATUS(status) == 43);
return 0;
}

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