Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753854AbbFVCc1 (ORCPT ); Sun, 21 Jun 2015 22:32:27 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:38113 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752362AbbFVCcS (ORCPT ); Sun, 21 Jun 2015 22:32:18 -0400 Date: Mon, 22 Jun 2015 03:32:07 +0100 From: Al Viro To: Eric Dumazet Cc: Mateusz Guzik , Andrew Morton , "Paul E. McKenney" , Yann Droneaud , Konstantin Khlebnikov , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] fs/file.c: don't acquire files->file_lock in fd_install() Message-ID: <20150622023207.GA24951@ZenIV.linux.org.uk> References: <20150420134326.GC2513@mguzik> <20150420151054.GD2513@mguzik> <1429550126.7346.268.camel@edumazet-glaptop2.roam.corp.google.com> <1429562991.7346.290.camel@edumazet-glaptop2.roam.corp.google.com> <1429639543.7346.329.camel@edumazet-glaptop2.roam.corp.google.com> <20150421200624.GA16097@mguzik> <20150421201201.GB16097@mguzik> <1429650413.18561.10.camel@edumazet-glaptop2.roam.corp.google.com> <1429678768.18561.64.camel@edumazet-glaptop2.roam.corp.google.com> <1430281503.3711.27.camel@edumazet-glaptop2.roam.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1430281503.3711.27.camel@edumazet-glaptop2.roam.corp.google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1553 Lines: 40 On Tue, Apr 28, 2015 at 09:25:03PM -0700, Eric Dumazet wrote: > @@ -553,11 +572,20 @@ void __fd_install(struct files_struct *files, unsigned int fd, > struct file *file) > { > struct fdtable *fdt; > - spin_lock(&files->file_lock); > - fdt = files_fdtable(files); > + > + rcu_read_lock_sched(); > + > + while (unlikely(files->resize_in_progress)) { > + rcu_read_unlock_sched(); > + wait_event(files->resize_wait, !files->resize_in_progress); > + rcu_read_lock_sched(); > + } > + /* coupled with smp_wmb() in expand_fdtable() */ > + smp_rmb(); > + fdt = rcu_dereference_sched(files->fdt); > BUG_ON(fdt->fd[fd] != NULL); > rcu_assign_pointer(fdt->fd[fd], file); > - spin_unlock(&files->file_lock); > + rcu_read_unlock_sched(); Umm... You've taken something that was safe to use in atomic contexts and turned into something that might wait for GFP_KERNEL allocation; what's to guarantee that no users get broken by that? At the very least, you want to slap might_sleep() in there - the actual sleep is going to be very rare, so it would be an extremely hard to reproduce and debug. AFAICS, all current in-tree users should be safe, but fd_install() is exported and quiet changes of that sort are rather antisocial. Generally I don't give a damn about out-of-tree code, but this one is over the top. I _think_ it's otherwise OK, but please, add might_sleep() *AND* a note in Documentation/filesystems/porting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/