On 05/31, Eric W. Biederman wrote: > > Oleg Nesterov <[email protected]> writes: > > > OK. But this means that even 1/3 is not 100% right, exactly because > > leader can be unhashed right before first_tid() takes rcu lock. Easy > > to fix, we should simply factor out the "nr != 0" check. > > > > And this also means that 3/3 is not right by the same reason. I'll > > make a simpler patch which only avoids the unnecessary get/put in > > proc_task_readdir(). > > > > Unless we can tolerate this very unlikely rase when the leader goes > > away after initial ENOENT check at the start, of course... Or unless > > we add canceldir() which resets getdents_callback->previous so that > > we could return ENOENT after filldir() was already called ;) > > A small race is fine and is fundamental to the process of readdir. > > The guarantee of open+readdir+close is that all directory entries that > exited before open and after close are returned. Directory entries that > are added or removed during the open+readir+close are returned at most > once. > > The important case to handle is when someone has opened the directory a > very long time ago or has chdir'd to the directory. With the result > the directory was removed before we start the readdir process entirely. > > If the tasks die in the narrow window while we are inside of readdir > races are impossible to avoid.
Ah OK. This means that v2 only needs the simple update. Thanks again Eric. Oleg. -- 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/
