Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753444AbcD0IgA (ORCPT ); Wed, 27 Apr 2016 04:36:00 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:34208 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752999AbcD0Ifd (ORCPT ); Wed, 27 Apr 2016 04:35:33 -0400 Date: Wed, 27 Apr 2016 10:35:30 +0200 From: Michal Hocko To: Mikulas Patocka Cc: linux-mm@kvack.org, Andrew Morton , LKML , Shaohua Li , dm-devel@redhat.com Subject: Re: [PATCH 17/19] dm: get rid of superfluous gfp flags Message-ID: <20160427083530.GD2179@dhcp22.suse.cz> References: <1460372892-8157-1-git-send-email-mhocko@kernel.org> <1460372892-8157-18-git-send-email-mhocko@kernel.org> <20160415130839.GJ32377@dhcp22.suse.cz> <20160416203135.GC15128@dhcp22.suse.cz> <20160422124730.GA11733@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4643 Lines: 112 [Adding dm-devel@redhat.com to CC] On Tue 26-04-16 13:20:04, Mikulas Patocka wrote: > On Fri, 22 Apr 2016, Michal Hocko wrote: [...] > > copy_params seems to be called only from the ioctl context which doesn't > > hold any locks which would lockup during the direct reclaim AFAICS. The > > git log shows that the code has used PF_MEMALLOC before which is even > > bigger mystery to me. Could you please clarify why this is GFP_NOIO > > restricted context? Maybe it needed to be in the past but I do not see > > any reason for it to be now so unless I am missing something the > > GFP_KERNEL should be perfectly OK. Also note that GFP_NOIO wouldn't work > > properly because there are copy_from_user calls in the same path which > > could page fault and do GFP_KERNEL allocations anyway. I can send follow > > up cleanups unless I am missing something subtle here. > > The LVM tool calls suspend and resume ioctls on device mapper block > devices. > > When a device is suspended, any bio sent to the device is held. If the > resume ioctl did GFP_KERNEL allocation, the allocation could get stuck > trying to write some dirty cached pages to the suspended device. > > The LVM tool and the dmeventd daemon use mlock to lock its address space, > so the copy_from_user/copy_to_user call cannot trigger a page fault. OK, I see, thanks for the clarification! This sounds fragile to me though. Wouldn't it be better to use the memalloc_noio_save for the whole copy_params instead? That would force all possible allocations to not trigger any IO. Something like the following. --- >From dbb2338bb88d2da1ff24cee59cbffd120b119e3b Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 27 Apr 2016 10:26:13 +0200 Subject: [PATCH] dm: clean up GFP_NIO usage copy_params uses GFP_NOIO for explicit allocation requests because this might be called from the suspend path. To quote Mikulas: : The LVM tool calls suspend and resume ioctls on device mapper block : devices. : : When a device is suspended, any bio sent to the device is held. If the : resume ioctl did GFP_KERNEL allocation, the allocation could get stuck : trying to write some dirty cached pages to the suspended device. : : The LVM tool and the dmeventd daemon use mlock to lock its address space, : so the copy_from_user/copy_to_user call cannot trigger a page fault. Relying on the mlock is quite fragile and we have a better way in kernel to enfore NOIO which is already used for the vmalloc fallback. Just use memalloc_noio_{save,restore} around the whole copy_params function which will force the same also to the page fult paths via copy_{from,to}_user. While we are there we can also remove __GFP_NOMEMALLOC because copy_params is never called from MEMALLOC context (e.g. during the reclaim). Signed-off-by: Michal Hocko --- drivers/md/dm-ioctl.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c index 2c7ca258c4e4..fe0b57d7573c 100644 --- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -1715,16 +1715,13 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern */ dmi = NULL; if (param_kernel->data_size <= KMALLOC_MAX_SIZE) { - dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); + dmi = kmalloc(param_kernel->data_size, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN); if (dmi) *param_flags |= DM_PARAMS_KMALLOC; } if (!dmi) { - unsigned noio_flag; - noio_flag = memalloc_noio_save(); - dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL); - memalloc_noio_restore(noio_flag); + dmi = __vmalloc(param_kernel->data_size, GFP_KERNEL | __GFP_HIGH | __GFP_HIGHMEM, PAGE_KERNEL); if (dmi) *param_flags |= DM_PARAMS_VMALLOC; } @@ -1801,6 +1798,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user) ioctl_fn fn = NULL; size_t input_param_size; struct dm_ioctl param_kernel; + unsigned noio_flag; /* only root can play with this */ if (!capable(CAP_SYS_ADMIN)) @@ -1832,9 +1830,12 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user) } /* - * Copy the parameters into kernel space. + * Copy the parameters into kernel space. Make sure that no IO is triggered + * from the allocation paths because this might be called during the suspend. */ + noio_flag = memalloc_noio_save(); r = copy_params(user, ¶m_kernel, ioctl_flags, ¶m, ¶m_flags); + memalloc_noio_restore(noio_flag); if (r) return r; -- 2.8.0.rc3 -- Michal Hocko SUSE Labs