Re: [PATCH 5.15] dm init: add dm-mod.waitfor to wait for asynchronously probed block devices

Greg KH
2023-07-21T07:03:00Z

On Fri, Jul 21, 2023 at 02:38:45PM +0800, Mark-PK Tsai wrote:
> > On Mon, Jul 17, 2023 at 09:57:28AM +0800, Mark-PK Tsai wrote:
> > > > On Sun, Jul 16, 2023, 11:16 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> > > >
> > > > > On Thu, Jul 13, 2023 at 01:58:37PM +0800, Mark-PK Tsai wrote:
> > > > > > From: Peter Korsgaard <peter@korsgaard.com>
> > > > > >
> > > > > > Just calling wait_for_device_probe() is not enough to ensure that
> > > > > > asynchronously probed block devices are available (E.G. mmc, usb), so
> > > > > > add a "dm-mod.waitfor=<device1>[,..,<deviceN>]" parameter to get
> > > > > > dm-init to explicitly wait for specific block devices before
> > > > > > initializing the tables with logic similar to the rootwait logic that
> > > > > > was introduced with commit cc1ed7542c8c ("init: wait for
> > > > > > asynchronously scanned block devices").
> > > > > >
> > > > > > E.G. with dm-verity on mmc using:
> > > > > > dm-mod.waitfor="PARTLABEL=hash-a,PARTLABEL=root-a"
> > > > > >
> > > > > > [ 0.671671] device-mapper: init: waiting for all devices to be
> > > > > available before creating mapped devices
> > > > > > [ 0.671679] device-mapper: init: waiting for device PARTLABEL=hash-a
> > > > > ...
> > > > > > [ 0.710695] mmc0: new HS200 MMC card at address 0001
> > > > > > [ 0.711158] mmcblk0: mmc0:0001 004GA0 3.69 GiB
> > > > > > [ 0.715954] mmcblk0boot0: mmc0:0001 004GA0 partition 1 2.00 MiB
> > > > > > [ 0.722085] mmcblk0boot1: mmc0:0001 004GA0 partition 2 2.00 MiB
> > > > > > [ 0.728093] mmcblk0rpmb: mmc0:0001 004GA0 partition 3 512 KiB,
> > > > > chardev (249:0)
> > > > > > [ 0.738274] mmcblk0: p1 p2 p3 p4 p5 p6 p7
> > > > > > [ 0.751282] device-mapper: init: waiting for device PARTLABEL=root-a
> > > > > ...
> > > > > > [ 0.751306] device-mapper: init: all devices available
> > > > > > [ 0.751683] device-mapper: verity: sha256 using implementation
> > > > > "sha256-generic"
> > > > > > [ 0.759344] device-mapper: ioctl: dm-0 (vroot) is ready
> > > > > > [ 0.766540] VFS: Mounted root (squashfs filesystem) readonly on
> > > > > device 254:0.
> > > > > >
> > > > > > Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
> > > > > > Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> > > > > > Cc: stable@vger.kernel.org
> > > > > > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
> > > > > > ---
> > > > > > .../admin-guide/device-mapper/dm-init.rst | 8 +++++++
> > > > > > drivers/md/dm-init.c | 22 ++++++++++++++++++-
> > > > > > 2 files changed, 29 insertions(+), 1 deletion(-)
> > > > >
> > > > > What is the git commit id of this change in Linus's tree?
> > > > >
> > > > > thanks,
> > > > >
> > > > > greg k-h
> > > > >
> > > > >
> > > >
> > > > Hey Greg,
> > > >
> > > > This change shouldn't be backported to stable@. It is a feature, if
> > > > Mark-PK feels they need it older kernels they need to carry the change
> > > > in their own tree. Or at a minimum they need to explain why this
> > > > change is warranted in stable@.
> > >
> > > Thanks for your comment.
> > > The reason why we think this should be backported to stable kernel is
> > > that it actually fix the potential race condition when make block
> > > device probe async in stable kernel.
> > > And we'd like to fix this upstream rather than just take it in
> > > our custom tree.
> >
> > Potential race condition, is this actually able to be hit in real life?
>
> Yes it hanppened, and it can lead the kernel init process stuck in
> the root wait loop.
>
> Below is the log.
> (I add 20 seconds delay in mtk_mci probe to quick reproduce it.)
>
> * Before apply this pactch
> [ 0.368594][ T1] device-mapper: init: waiting for all devices to be available before creating mapped devices
> [ 21.673047][ T45] probe of 1c660000.mtk-mmc-fcie returned 0 after 21541020 usecs
> [ 21.673061][ T45] mtk_mci 1c660000.mtk-mmc-fcie: driver mtk_mci async attach completed: 0
> [ 21.680006][ T1] device-mapper: table: 254:0: verity: Data device lookup failed <--------------- start after mtk_mci probe done
> [ 21.680012][ T1] device-mapper: ioctl: error adding target to table <--------------------------- won't create /dev/dm-0
> [ 21.680067][ T67] mmc0: new HS400 Enhanced strobe MMC card at address 0001
> [ 21.680184][ T67] bus: 'mmc': __driver_probe_device: matched device mmc0:0001 with driver mmcblk
> [ 21.680192][ T67] bus: 'mmc': really_probe: probing driver mmcblk with device mmc0:0001
> [ 21.680500][ T67] mmcblk0: mmc0:0001 016G01 14.5 GiB
> [ 21.683404][ T67] mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 p15 p16 p17 p18 p19 p20 p21 p22 p23 p24 p25 p26 p27 p28 p29
> [ 21.686152][ T67] mmcblk0boot0: mmc0:0001 016G01 8.00 MiB
> [ 21.687166][ T67] mmcblk0boot1: mmc0:0001 016G01 8.00 MiB
> [ 21.687955][ T67] mmcblk0rpmb: mmc0:0001 016G01 4.00 MiB, chardev (238:0)
> [ 21.687977][ T67] driver: 'mmcblk': driver_bound: bound to device 'mmc0:0001'
> [ 21.688004][ T67] bus: 'mmc': really_probe: bound device mmc0:0001 to driver mmcblk
> [ 21.688010][ T67] probe of mmc0:0001 returned 0 after 7819 usecs
> [ 21.688166][ T1] Waiting for root device /dev/dm-0...
> [ 41.023192][ T1] driver_probe_done: probe_count = 0
> ... can't exit from the root wait loop
>
> * After apply this patch and add dm-mod.waitfor="PARTLABEL=rootfs"
> [ 0.368417][ T1] device-mapper: init: waiting for all devices to be available before creating mapped devices
> [ 21.672749][ T45] probe of 1c660000.mtk-mmc-fcie returned 0 after 21540992 usecs
> [ 21.672767][ T45] mtk_mci 1c660000.mtk-mmc-fcie: driver mtk_mci async attach completed: 0
> [ 21.672774][ T1] device-mapper: init: waiting for device PARTLABEL=rootfs ...
> [ 21.672869][ T43] mtk_mci 1c660000.mtk-mmc-fcie: eMMC: HS400 5.1 200MHz
> [ 21.679743][ T43] mmc0: new HS400 Enhanced strobe MMC card at address 0001
> [ 21.679852][ T43] bus: 'mmc': __driver_probe_device: matched device mmc0:0001 with driver mmcblk
> [ 21.679858][ T43] bus: 'mmc': really_probe: probing driver mmcblk with device mmc0:0001
> [ 21.680204][ T43] mmcblk0: mmc0:0001 016G01 14.5 GiB
> [ 21.682866][ T43] mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 p15 p16 p17 p18 p19 p20 p21 p22 p23 p24 p25 p26 p27 p28 p29
> [ 21.685579][ T43] mmcblk0boot0: mmc0:0001 016G01 8.00 MiB
> [ 21.686631][ T43] mmcblk0boot1: mmc0:0001 016G01 8.00 MiB
> [ 21.687533][ T43] mmcblk0rpmb: mmc0:0001 016G01 4.00 MiB, chardev (238:0)
> [ 21.687559][ T43] driver: 'mmcblk': driver_bound: bound to device 'mmc0:0001'
> [ 21.687585][ T43] bus: 'mmc': really_probe: bound device mmc0:0001 to driver mmcblk
> [ 21.687591][ T43] probe of mmc0:0001 returned 0 after 7732 usecs
> [ 21.687838][ T1] device-mapper: init: all devices available <---------------------------------- start after PARTLABEL=rootfs is ready
> [ 21.688155][ T1] device-mapper: verity: sha1 using implementation "sha1-generic"
> [ 21.688975][ T1] device-mapper: ioctl: dm-0 (dm-verity) is ready
>

Ok, seems sane, I'll queue this up for 6.1.y and 5.15.y now.

thanks,

greg k-h