Oleg Nesterov <[email protected]> writes: > On 09/08, Eric W. Biederman wrote: >> >> Oleg Nesterov <[email protected]> writes: >> >> > On 09/08, Oleg Nesterov wrote: >> >> >> >> Off topic. What if the first alloc_pid() succeeds and then later >> >> copy_process() fails. In this case free_pid() is called but >> >> PIDNS_HASH_ADDING was not cleared, we miss kern_unmount(), no? >> > >> > Perhaps something like below? >> >> I am thinking more: >> >> diff --git a/kernel/pid.c b/kernel/pid.c >> index ab75add..ef59516 100644 >> --- a/kernel/pid.c >> +++ b/kernel/pid.c >> @@ -273,6 +273,10 @@ void free_pid(struct pid *pid) >> */ >> wake_up_process(ns->child_reaper); >> break; >> + case PIDNS_HASH_ADDING: >> + /* Handle a fork failure of the first process */ >> + ns->nr_hashed = 0; > > Agreed, it also makes sense to clear ->nr_hashed. But I still think > that WARN_ON(ns->child_reaper) makes sense too.
I don't know that I like warnings for impossible conditions. How could we even make a mistake that gets us there? >> At which point I ask myself what of the pathlogocical case where the >> first fork fails but because we created the pid namespace with unshare >> there is a concurrent fork from another process into the pid namespace >> that succeeds. Resulting in one pid in the pid namespace that is not >> the reaper. > > But how can setns() work before the first fork() succeeds and makes the > ->child_reaper visible in /proc ? > > Probably I missed something obvious, I didn't sleep today... Actually that is a very good point. That is an accidental feature but one I very much appreciate today. Of course this leads me to the question of what the checkpoint/restart guys can do about checkpointing that properly. Sigh. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
