On 09/03, Al Viro wrote: > > When tracer exits, everything that had been ptraced by it > gets its ->ptrace reset to 0 and woken up to run. Fine, but... > what should happen if the last thing that had been done to the > child was PTRACE_SINGLESTEP?
Yes. If the tracer exits "unexpectedly", it can leave the tracee in the inconsistent state. IIRC, we already discussed this, but I can't recall the result. > Is that a bug or deliberate > behaviour? This is not easy to fix. ptrace_disable() and user_disable_single_step() is arch dependant, but at least on x86 it assumes that the tracee is not running, so exit_ptrace() can't do this. And (iirc) it can even sleep, but this is fixable. We can change exit_ptrace() to drop/re-acquire tasklist. And this also complicates PTRACE_DETACH_ASYNC which (imho) we need. Currently the tracer can't detach the running tracee. And worse, it can't detach a zombie. It should do wait() but if this process has alive sub-threads it can do nothing. This is another reason to move enable/disable step into ptrace_stop(). And in fact I had the patches a loong ago, but we need to cleanup the usage of PT_SINGLESTEP/PT_BLOCKSTEP first. The tracer should simply set/clear these PT_ flags and resume the tracee which should check them and do user_*_single_step() in response. But. Whatever we do, exit_ptrace() can race with SIGTRAP anyway. > Related question: should execve(2) clear (ptrace-inflicted) > singlestepping? Perhaps, but > Tracer > exit(), however, does *not* do that right now, so the state after > execve(2) is theoretically observable. ... why execve() is special? Olef. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/