On 3/2/16, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Mar 2, 2016 at 6:55 AM, Andrea Arcangeli <aarcange@xxxxxxxxxx> > wrote: >> >> Running page faults that late in the exit path with signal disabled >> was frankly unexpected. > > I agree that it's less than wonderful. > >> Apparently it's not just >> PF_EXITING that prevents SIGKILL to reach handle_userfault(). The >> below change still didn't allow to kill the task: >> >> + exit_futex(tsk); /* run before setting PF_EXITING */ >> exit_signals(tsk); /* sets PF_EXITING */ > > It's not just "exit_futex()" (what is that? I assume you mean > exit_robust_list()) that triggers the problem, it's also the > > put_user(0, tsk->clear_child_tid); > > in mm_release(). > > So it's not just about futexes. > > The might be other final user space accesses lurking too that I didn't > even think about. > > Anyway, I committed (a) as the safest version with the least side > effects. If people think some more about this and come up with > solutions how to avoid these kinds of "very late user space accesses" > cleanly, I think that would be great. > Is that commit [1] Linux-4.5 material or affects other versions, too? commit 39680f50ae54cbbb6e72ac38b8329dd3eb9105f4 "userfaultfd: don't block on the last VM updates at exit time" - Sedat - [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=39680f50ae54cbbb6e72ac38b8329dd3eb9105f4 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
