]> nv-tegra.nvidia Code Review - linux-2.6.git/commit
ptrace_detach: the wrong wakeup breaks the ERESTARTxxx logic
authorOleg Nesterov <oleg@redhat.com>
Thu, 2 Apr 2009 23:58:21 +0000 (16:58 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 3 Apr 2009 02:05:00 +0000 (19:05 -0700)
commit95a3540da9c81a5987be810e1d9a83640a366bd5
treed5143f232f885f6aa8829288dc0ceb2cd9e6e34e
parentbb24c679a51b1a9b726b901330649e3861814ac0
ptrace_detach: the wrong wakeup breaks the ERESTARTxxx logic

Another ancient bug. Consider this trivial test-case,

int main(void)
{
int pid = fork();

if (pid) {
ptrace(PTRACE_ATTACH, pid, NULL, NULL);
wait(NULL);
ptrace(PTRACE_DETACH, pid, NULL, NULL);
} else {
pause();
printf("WE HAVE A KERNEL BUG!!!\n");
}

return 0;
}

the child must not "escape" for sys_pause(), but it can and this was seen
in practice.

This is because ptrace_detach does:

if (!child->exit_state)
wake_up_process(child);

this wakeup can happen after this child has already restarted sys_pause(),
because it gets another wakeup from ptrace_untrace().

With or without this patch, perhaps sys_pause() needs a fix.  But this
wakeup also breaks the SIGNAL_STOP_STOPPED logic in ptrace_untrace().

Remove this wakeup.  The caller saw this task in TASK_TRACED state, and
unless it was SIGKILL'ed in between __ptrace_unlink()->ptrace_untrace()
should handle this case correctly.  If it was SIGKILL'ed, we don't need to
wakup the dying tracee too.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/ptrace.c