On Tue, 23 Aug 2022 09:49:11 -0400 Jes Sorensen <jes@xxxxxxxxxxxxxxxxxx> wrote: > On 7/20/22 04:20, Mariusz Tkaczyk wrote: > > On Tue, 19 Jul 2022 10:43:06 -0600 > > Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote: > > > >> On 2022-07-19 05:27, Mariusz Tkaczyk wrote: > >>> On Fri, 15 Jul 2022 10:20:26 +0800 > >>> Guoqing Jiang <guoqing.jiang@xxxxxxxxx> wrote: > >>>> On 7/15/22 6:37 AM, Logan Gunthorpe wrote: > >>>>> To fix this, don't bother trying to open the md device for CREATE and > >>>>> ASSEMBLE commands, as the file descriptor will never be used anyway > >>>>> even if it is successfully openned. > >>> Hi All, > >>> > >>> This is not a fix, it just reduces race probability because file > >>> descriptor will be opened later. > >> > >> That's not correct. The later "open" call actually will use the new_array > >> parameter which will wait for the workqueue before creating a new array > >> device, so the old one is properly cleaned up and there is no longer > >> a race condition with this patch. If new_array doesn't exist and it falls > >> back to a regular open, then it will still do the right thing and open the > >> device with create_on_open. > > > > Array is created by /sys/module/md/parameters/new_array if chosen_name has > > certain form. For IMSM, when we are creating arrays using "/dev/md/name" or > > "name" only create_on_open is used (if no "names=yes" in config). I > > understand that it works with tests but I don't feel that it is complete > > yet. Could you how it behaves when we use "whatever"? > > > > #mdadm -CR whatever -l0 -n2 /dev/nvme[01]n1 > > > > Please do not use --name= parameter. > > > > I want to disable create_on_open and always use new_array in the future, > > without fallback to create_on_open possibility. So I would like to have > > solution which is not relying on it. > >> > >>> I tried to resolve it in the past by adding completion to md driver and > >>> force mdadm --stop command to wait for sysfs clean up but I have never > >>> finished it. IMO it is a better way, wait for device to be fully removed > >>> by MD during stop. Thoughts? > >> > >> I don't think that would work very well. Userspace would end up blocking > >> on --stop indefinitely if there are any references delaying cleanup to > >> the device. That's not very user friendly. Given that opening the md > >> device has side-effects, I think we should avoid opening when we > >> should know that we are about to try to create a new device. > > > > Got it, thanks! > > > > Hmm, so maybe the existing MD device should be marked as "in the middle of > > removal" somehow to gives mdadm possibility to detect that. If we are using > > node as name "/dev/mdX" then we will need to throw error, but when node > > needs to be determined by find_free_devnm() then it will simply skip this > > one and gives next one. But it will require changes in kernel probably. > > > >> > >>> One objection I have here is that error handling is changed, so it could > >>> be harmful change for users. > >> > >> Hmm, yes seems like I was a bit sloppy here. However, it still seems > >> possible to fix this up by not pre-opening the device. The only use for > >> the mdfd in CREATE, ASSEMBLE and BUILD is to get the minor number if > >> ident.super_minor == -2 and check if an existing specified device is an md > >> device (which may be redundant). We could replace this with a stat() call > >> to avoid opening the device. What about the patch at the end of this > >> email? > > > > LGTM, I put small comment. But as I said before, probably it don't fix all > > creation cases. > > Hi Mariusz, > > Just to recap on this, do you support applying this patch as is, or > should we wait for the longer term fix you were mentioning? > Hi Jes, This patch looks good. Please apply next one version: https://lore.kernel.org/linux-raid/20220727215246.121365-3-logang@xxxxxxxxxxxx/ Thanks, Mariusz
