From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751201AbdEaJTK (ORCPT ); Wed, 31 May 2017 05:19:10 -0400 Received: from mx2.suse.de ([195.135.220.15]:36399 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751070AbdEaJTJ (ORCPT ); Wed, 31 May 2017 05:19:09 -0400 Date: Wed, 31 May 2017 11:19:05 +0200 From: Michal Hocko To: Omar Sandoval Cc: kernel test robot , Vinnie Magro , David Sterba , Omar Sandoval , LKML , Stephen Rothwell , lkp@01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Message-ID: <20170531091904.GD27783@dhcp22.suse.cz> References: <20170531063033.GC1795@yexl-desktop> <20170531065128.GB3853@dhcp22.suse.cz> <20170531091202.GA769@vader> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170531091202.GA769@vader> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 31-05-17 02:12:02, Omar Sandoval wrote: > On Wed, May 31, 2017 at 08:51:28AM +0200, Michal Hocko wrote: > > On Wed 31-05-17 14:30:33, kernel test robot wrote: > > > > > > FYI, we noticed the following commit: > > > > > > commit: beeeccca9bebcec386cc31c250cff8a06cf27034 ("btrfs: Use kvzalloc instead of kzalloc/vmalloc in alloc_bitmap") > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master > > > > I have intentionally skipped alloc_bitmap because it relies on GFP_NOFS. > > This doesn't work properly when falling back to vmalloc and that is what > > the warning reported here says. I believe the right approach is to check > > whether the GFP_NOFS is _really_ needed and document why if yes. > > Otherwise drop the NOFS part in one patch with the explanation and > > convert it to kvmalloc in a separate patch. > > Unfortunately we really do need GFP_NOFS here, the free space tree is > modified while we are committing a fs transaction, sometimes in the > critical section when we block new operations from joining the > transaction. OK, please document this. > Looking at the comment in kvmalloc_node(): > > /* > * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables) > * so the given set of flags has to be compatible. > */ > WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); > > has alloc_bitmap() always been broken by virtue of calling vmalloc() > with GFP_NOFS? yes. vmalloc is simply not GFP_NOFS safe as it performs GFP_KERNEL hardcoded allocations. The way out of this is to use memalloc_nofs_{save,restore} around kvmalloc call. -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============1723886715483527737==" MIME-Version: 1.0 From: Michal Hocko To: lkp@lists.01.org Subject: Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc_node Date: Wed, 31 May 2017 11:19:05 +0200 Message-ID: <20170531091904.GD27783@dhcp22.suse.cz> In-Reply-To: <20170531091202.GA769@vader> List-Id: --===============1723886715483527737== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Wed 31-05-17 02:12:02, Omar Sandoval wrote: > On Wed, May 31, 2017 at 08:51:28AM +0200, Michal Hocko wrote: > > On Wed 31-05-17 14:30:33, kernel test robot wrote: > > > = > > > FYI, we noticed the following commit: > > > = > > > commit: beeeccca9bebcec386cc31c250cff8a06cf27034 ("btrfs: Use kvzallo= c instead of kzalloc/vmalloc in alloc_bitmap") > > > https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git mast= er > > = > > I have intentionally skipped alloc_bitmap because it relies on GFP_NOFS. > > This doesn't work properly when falling back to vmalloc and that is what > > the warning reported here says. I believe the right approach is to check > > whether the GFP_NOFS is _really_ needed and document why if yes. > > Otherwise drop the NOFS part in one patch with the explanation and > > convert it to kvmalloc in a separate patch. > = > Unfortunately we really do need GFP_NOFS here, the free space tree is > modified while we are committing a fs transaction, sometimes in the > critical section when we block new operations from joining the > transaction. OK, please document this. > Looking at the comment in kvmalloc_node(): > = > /* > * vmalloc uses GFP_KERNEL for some internal allocations (e.g page table= s) > * so the given set of flags has to be compatible. > */ > WARN_ON_ONCE((flags & GFP_KERNEL) !=3D GFP_KERNEL); > = > has alloc_bitmap() always been broken by virtue of calling vmalloc() > with GFP_NOFS? yes. vmalloc is simply not GFP_NOFS safe as it performs GFP_KERNEL hardcoded allocations. The way out of this is to use memalloc_nofs_{save,restore} around kvmalloc call. -- = Michal Hocko SUSE Labs --===============1723886715483527737==--