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Date:   Fri, 22 Jul 2022 18:30:13 +0800
From:   lijiazi <jqqlijiazi@gmail.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        "Jiazi.Li" <jiazi.li@transsion.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] driver core: Do not add a device that has been removed
 in device_shutdown to devices_kset list again.
Message-ID: <20220722101008.GA2223@Jiazi.Li>
References: <20220721123325.4675-1-jiazi.li@transsion.com>
 <Ytmlih/TgGNrRTwy@kroah.com>
 <20220722061246.GA4801@Jiazi.Li>
 <YtpJg90L0OUxa5DS@kroah.com>
 <20220722072903.GA5390@Jiazi.Li>
 <YtpXYzMPje44SdyE@kroah.com>
 <20220722082242.GA5656@Jiazi.Li>
 <Ytpif4TmTEaDklbW@kroah.com>
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On Fri, Jul 22, 2022 at 10:40:31AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Jul 22, 2022 at 04:22:42PM +0800, lijiazi wrote:
> > On Fri, Jul 22, 2022 at 09:53:07AM +0200, Greg Kroah-Hartman wrote:
> > > On Fri, Jul 22, 2022 at 03:31:19PM +0800, lijiazi wrote:
> > > > On Fri, Jul 22, 2022 at 08:53:55AM +0200, Greg Kroah-Hartman wrote:
> > > > > On Fri, Jul 22, 2022 at 02:18:11PM +0800, lijiazi wrote:
> > > > > > On Thu, Jul 21, 2022 at 09:14:18PM +0200, Greg Kroah-Hartman wrote:
> > > > > > > On Thu, Jul 21, 2022 at 08:33:25PM +0800, Jiazi.Li wrote:
> > > > > > > > There is a race between device_shutdown and devices_kset_move_last:
> > > > > > > > 1. device_shutdown remove dev from devices_kset, unlock list_lock
> > > > > > > > 
> > > > > > > > 2. supplier call device_link_add move this consummer dev to
> > > > > > > > last of devices_kset:
> > > > > > > > devices_kset_move_last+0x184/0x1fc
> > > > > > > > device_reorder_to_tail+0x50/0x17c
> > > > > > > > device_link_add+0x670/0x9c0
> > > > > > > > phy_get+0x88/0x300
> > > > > > > > 
> > > > > > > > 3. device_shutdown call dev->bus->shutdown first time
> > > > > > > > 
> > > > > > > > 4. in next loop, device_shutdown pick this dev from devices_kset
> > > > > > > > again, and call dev->bus->shutdown for the second time.
> > > > > > > > 
> > > > > > > > If the protection mechanism of dev->bus->shutdown is not perfect,
> > > > > > > > the following crash will occur:
> > > > > > > > [37.366651] [T1000001] Unable to handle kernel NULL pointer
> > > > > > > > dereference at virtual address 0000000000000070
> > > > > > > > [37.414053] [T1600001] Kernel Offset: 0x2c73800000 from 0xffffffc010000000
> > > > > > > > [37.414908] [T1600001] PHYS_OFFSET: 0x40000000
> > > > > > > > [37.415458] [T1600001] pstate: 60400005 (nZCv daif +PAN -UAO)
> > > > > > > > [37.416172] [T1600001] pc : [0xffffffec83eccd40] kernfs_find_ns+0x18/0x154
> > > > > > > > [37.417025] [T1600001] lr : [0xffffffec83ed8714] sysfs_unmerge_group+0x70/0x2e0
> > > > > > > > [37.417931] [T1600001] sp : ffffffc01008ba90
> > > > > > > > [37.418456] [T1600001] x29: ffffffc01008ba90 x28: ffffffec863c1000
> > > > > > > > [37.419221] [T1600001] x27: ffffffec85234e30 x26: ffffffec86490000
> > > > > > > > [37.419985] [T1600001] x25: ffffff80c854a4c0 x24: ffffff80c854a428
> > > > > > > > [37.420750] [T1600001] x23: 0000000000400100 x22: ffffffec85c4c5c8
> > > > > > > > [37.421514] [T1600001] x21: ffffffec85c4c5a0 x20: 0000000000000000
> > > > > > > > [37.422277] [T1600001] x19: ffffff80c0178000 x18: ffffffc010083068
> > > > > > > > [37.423043] [T1600001] x17: 0000000000000000 x16: 00000000000000d8
> > > > > > > > [37.423807] [T1600001] x15: ffffffec842b9314 x14: ffffffec85b04050
> > > > > > > > [37.424572] [T1600001] x13: 0000000000000000 x12: 000000000000000a
> > > > > > > > [37.425336] [T1600001] x11: 0000000000000000 x10: ffffffec863e9000
> > > > > > > > [37.426102] [T1600001] x9 : 0000000000000001 x8 : 0000000000000000
> > > > > > > > [37.426869] [T1600001] x7 : 332e37332020205b x6 : ffffffec863e6e7e
> > > > > > > > [37.427633] [T1600001] x5 : ffffffffffffffff x4 : 0000000000000000
> > > > > > > > [37.428396] [T1600001] x3 : 000000000000003c x2 : 0000000000000000
> > > > > > > > [37.429161] [T1600001] x1 : ffffffec85c4c5c8 x0 : 0000000000000000
> > > > > > > > [37.612410] [T1600001] Call trace:
> > > > > > > > [37.612831] [T1600001]  dump_backtrace.cfi_jt+0x0/0x8
> > > > > > > > [37.613457] [T1600001]  dump_stack_lvl+0xc4/0x140
> > > > > > > > [37.614038] [T1600001]  dump_stack+0x1c/0x2c
> > > > > > > > [37.614588] [T1600001]  mrdump_common_die+0x3a8/0x544 [mrdump]
> > > > > > > > [37.615326] [T1600001]  ipanic_die+0x24/0x38 [mrdump]
> > > > > > > > [37.615951] [T1600001]  die+0x344/0x748
> > > > > > > > [37.616425] [T1600001]  die_kernel_fault+0x84/0x94
> > > > > > > > [37.617016] [T1600001]  __do_kernel_fault+0x230/0x27c
> > > > > > > > [37.617642] [T1600001]  do_page_fault+0xb4/0x754
> > > > > > > > [37.618212] [T1600001]  do_translation_fault+0x48/0x64
> > > > > > > > [37.618846] [T1600001]  do_mem_abort+0x6c/0x164
> > > > > > > > [37.619406] [T1600001]  el1_abort+0x44/0x68
> > > > > > > > [37.619921] [T1600001]  el1_sync_handler+0x58/0x88
> > > > > > > > [37.620512] [T1600001]  el1_sync+0x8c/0x140
> > > > > > > > [37.621028] [T1600001]  kernfs_find_ns+0x18/0x154
> > > > > > > > [37.621608] [T1600001]  sysfs_unmerge_group+0x70/0x2e0
> > > > > > > > [37.622246] [T1600001]  device_del+0x198/0xd00
> > > > > > > > [37.622794] [T1600001]  device_unregister+0x1c/0x3c
> > > > > > > > [37.623409] [T1600001]  charger_device_unregister+0x40/0x54 [charger_class]
> > > > > > > > [37.624277] [T1600001]  sgm41516d_shutdown+0x54/0x84 [sgm41516d]
> > > > > > > > [37.625021] [T1600001]  i2c_device_shutdown+0x68/0x118
> > > > > > > > [37.625656] [T1600001]  device_shutdown+0x234/0x614
> > > > > > > > [37.626259] [T1600001]  kernel_restart+0x74/0x1e8
> > > > > > > > [37.626840] [T1600001]  __arm64_sys_reboot+0x3b0/0x424
> > > > > > > > [37.627475] [T1600001]  el0_svc_common+0xd4/0x270
> > > > > > > > [37.628056] [T1600001]  el0_svc+0x28/0x88
> > > > > > > > [37.628549] [T1600001]  el0_sync_handler+0x8c/0xf0
> > > > > > > > [37.629141] [T1600001]  el0_sync+0x1b4/0x1c0
> > > > > > > > 
> > > > > > > > because dev->kobject.sd has been set to NULL in fisrt shutdown.
> > > > > > > 
> > > > > > > We can't take kernel changes to fix bugs in out-of-tree kernel modules.
> > > > > > > Can you reproduce this with the in-tree drivers?  If so, which ones?
> > > > > > > 
> > > > > > > thanks,
> > > > > > > 
> > > > > > > greg k-h
> > > > > > 
> > > > > > I'm sorry, I am working on mobile phone base on android12+GKI2.0.
> > > > > > So far, I found two charger driver have this issue , maybe more.
> > > > > > Reproduce method is plug/unplug usb cable when device shutdown or
> > > > > > reboot.
> > > > > > GKI2.0 requires that most vendor's drivers are out-of-tree modules.
> > > > > 
> > > > > That is not true, Google would much rather accept in-tree modules that
> > > > > are upstream.  It's your choice to not submit them for inclusion, please
> > > > > don't pass the blame to someone else.
> > > > > 
> > > > 
> > > > You are right.
> > > > > > I haven't found in-tree drivers has this issue.
> > > > > 
> > > > > Then perhaps your drivers are broken?  Do you have a link to the source
> > > > > anywhere?
> > > > 
> > > > Yes, as I said earlier, I have encountered two broken drivers.
> > > > Sorry for can't provide a link.
> > > 
> > > Why not, the license of your driver is GPLv2, right?
> > > 
> > 
> > The driver is GPLv2, but for some other reason.
> 
> What other reason?
> 

For confidentiality reasons, company prohibits uploading codes to github
and other websites.
> > > > Instead of fix driver one by one, perhaps add a list_empty check is
> > > > a better method.
> > > 
> > > Please work to find the problem in your driver first.  We do not add
> > > "hardening" code to the kernel core to prevent buggy drivers from
> > > causing problems, for obvious reasons.
> > > 
> > 
> > I have fixed the problem in vendor's driver, but I can't stop them from
> > make similar mistake.
> 
> What was the problem that it had?  Perhaps post that here for us to see
> what was required to resolve this.

In i2c device driver's shutdown callback, do not set i2c_client->dev
->drvdata to NULL.
1. device_shutdown remove device from devices_kset and call shutdown
2. During the shutdown or reboot of phone, if plug/unplug usb, driver call
phy_get to obtain a reference to usb phy.
phy_get
  ->device_link_add//i2c device as usb phy's consumer
    ->device_reorder_to_tail
      ->device_kset_move_last//move i2c device to last of devices_kset
3. device_shutdown call i2c device shutdown again
My workaround is set i2c_clinet->dev->drvdata to NULL before return in
shutdown callback, and check whether drvdata is NULL at the beginning of
shutdown callback, if NULL, just return.

But this cannot prevent shutdown from being called twice.

> 
> thanks,
> 
> greg k-h