RE: Lockdep warning caused by "driver core: Fix sleeping in invalid context during device link deletion"

[Peng Fan <peng.fan@nxp.com>]

> Subject: Re: Lockdep warning caused by "driver core: Fix sleeping in invalid
> context during device link deletion"
> 
> On Wed, Aug 26, 2020 at 10:17 PM Saravana Kannan
> <saravanak@google.com> wrote:
> >
> > On Thu, Aug 20, 2020 at 8:50 PM Dong Aisheng <dongas86@gmail.com>
> wrote:
> > >
> > > Hi ALL,
> > >
> > > We met the below WARNING during system suspend on an iMX6Q SDB
> board
> > > with the latest linus/master branch (v5.9-rc1+) and next-20200820.
> > > v5.8 kernel is ok. So i did bisect and finally found it's caused by
> > > the patch below.
> > > Reverting it can get rid of the warning, but I wonder if there may
> > > be other potential issues.
> > > Any ideas?
> > >
> > > Defconfig used is: imx_v6_v7_defconfig
> > >
> >
> > ----- 8< ----- Snipped text that was a bit misleading
> >
> > >
> > > Error log:
> > > # echo mem > /sys/power/state
> > > [   39.111865] PM: suspend entry (deep)
> > > [   39.148650] Filesystems sync: 0.032 seconds
> > > [   39.154034]
> > > [   39.155537]
> ======================================================
> > > [   39.161723] WARNING: possible circular locking dependency detected
> > > [   39.167911] 5.9.0-rc1-00103-g7eac66d0456f #37 Not tainted
> > > [   39.173315] ------------------------------------------------------
> > > [   39.179500] sh/647 is trying to acquire lock:
> > > [   39.183862] c15a310c (dpm_list_mtx){+.+.}-{3:3}, at:
> > > dpm_for_each_dev+0x20/0x5c
> > > [   39.191200]
> > > [   39.191200] but task is already holding lock:
> > > [   39.197036] c15a37e4 (fw_lock){+.+.}-{3:3}, at:
> fw_pm_notify+0x90/0xd4
> > > [   39.203582]
> > > [   39.203582] which lock already depends on the new lock.
> > > [   39.203582]
> > > [   39.211763]
> > > [   39.211763] the existing dependency chain (in reverse order) is:
> > > [   39.219249]
> > > [   39.219249] -> #2 (fw_lock){+.+.}-{3:3}:
> > > [   39.224673]        mutex_lock_nested+0x1c/0x24
> > > [   39.229126]        firmware_uevent+0x18/0xa0
> > > [   39.233411]        dev_uevent+0xc4/0x1f8
> > > [   39.237343]        uevent_show+0x98/0x114
> > > [   39.241362]        dev_attr_show+0x18/0x48
> > > [   39.245472]        sysfs_kf_seq_show+0x84/0xec
> > > [   39.249927]        seq_read+0x138/0x550
> > > [   39.253774]        vfs_read+0x94/0x164
> > > [   39.257529]        ksys_read+0x60/0xe8
> > > [   39.261288]        ret_fast_syscall+0x0/0x28
> > > [   39.265564]        0xbed7c808
> > > [   39.268538]
> > > [   39.268538] -> #1 (kn->active#3){++++}-{0:0}:
> > > [   39.274391]        kernfs_remove_by_name_ns+0x40/0x94
> > > [   39.279450]        device_del+0x144/0x3fc
> >
> > Rafael/Greg,
> >
> > I'm not very familiar with the #0 and #2 calls stacks. But poking
> > around a bit, they are NOT due to the device-link-device. But the new
> > stuff is the above two lines that are deleting the device-link-device
> > (that's used to expose device link details in sysfs) when the device
> > link is deleted.
> >
> > Kicking off a workqueue to break this cycle is easy, but the problem
> > is that if I queue a work to delete the device, then the sysfs folder
> > won't get removed immediately. And if the same link is created again
> > before the work is completed, then there'll be a sysfs name collision
> > and warning.
> >
> > So, I'm kinda stuck here. Open to suggestions. Hoping you'll have
> > better ideas for breaking the cycle. Or point out how I'm
> > misunderstanding the cycle here.
> >
> 
> Aisheng,
> 
> Sent out a fix that I think should work.
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flkml%2F20200831221007.1506441-1-saravanak%40google.com%
> 2FT%2F%23u&amp;data=02%7C01%7Cpeng.fan%40nxp.com%7C3254604d7
> 41b4d1ce73b08d84dfb65af%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
> %7C0%7C637345089428077609&amp;sdata=5lh8WO%2BYMh4C1sBn58Fsm
> XsjqjPj%2B%2FB71%2FENfMGDtTk%3D&amp;reserved=0
> 
> I wasn't able to reproduce it in my hardware. So, if you can test that patch
> (and respond to that thread), that'd be great.

I not found your patch in my mailbox, but anyway I tested it.

Tested-by: Peng Fan <peng.fan@nxp.com> (i.MX7ULP EVK)

Regards,
Peng.

> 
> -Saravana