Re: Crashes in 5.15-git in i2c code

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Linus -- FYI since I'm sure you'll see more reports of this; we
call driver resume methods before they're prepared for it.  We'll fix
or revert this ASAP.]

On Mon, Nov 08, 2021 at 12:58:25PM -0600, Bjorn Helgaas wrote:
> [+cc Uwe, Rafael, linux-pm, linux-pci, linux-kernel, beginning of
> thread: https://lore.kernel.org/linux-i2c/CAP145pgdrdiMAT7=-iB1DMgA7t_bMqTcJL4N0=6u8kNY3EU0dw@mail.gmail.com/T/#t]
> 
> On Mon, Nov 08, 2021 at 05:34:14PM +0100, Robert Święcki wrote:
> > > I'm daily-driving the linux from Linus' git (recompiling every day or
> > > two), and yesterday it stopped booting. Below is the dmesg from
> > > pstore.
> > > ...
> > 
> > This introduced the bug: 0c5c62ddf88c34bc83b66e4ac9beb2bb0e1887d4
> > https://github.com/torvalds/linux/commit/0c5c62ddf88c34bc83b66e4ac9beb2bb0e1887d4
> 
> Thank you very much for the debugging and this report!  This report is
> for i2c, but the problem will affect many drivers.
> 
> > > <1>[    1.431369][  T447] BUG: kernel NULL pointer dereference,
> > > address: 0000000000000540
> > > <1>[    1.431371][  T447] #PF: supervisor read access in kernel mode
> > > <1>[    1.431375][  T447] #PF: error_code(0x0000) - not-present page
> > > <6>[    1.431378][  T447] PGD 0 P4D 0
> > > <4>[    1.431384][  T447] Oops: 0000 [#1] PREEMPT SMP NOPTI
> > > <4>[    1.431388][  T447] CPU: 12 PID: 447 Comm: systemd-udevd
> > > Tainted: G            E     5.15.0+ #91
> > > <4>[    1.431391][  T447] Hardware name: ASUS System Product Name/ROG
> > > CROSSHAIR VIII FORMULA, BIOS 3801 07/30/2021
> > > <4>[    1.431392][  T447] RIP: 0010:i2c_dw_pci_resume+0x8/0x40
> > > [i2c_designware_pci]
> > > <4>[    1.431399][  T447] Code: 00 00 00 00 66 66 2e 0f 1f 84 00 00 00
> > > 00 00 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 84 00 00 00 00 00 53 48
> > > 8b 5f 78 48 89 df <ff> 93 40 05 00 00 c6 83 c0 05 00 00 00 5b c3 66 66
> > > 2e 0f 1f 84 00
> > > <4>[    1.431401][  T447] RSP: 0018:ffffb3e740a13ba8 EFLAGS: 00010286
> > > <4>[    1.431403][  T447] RAX: 0000000000000000 RBX: 0000000000000000
> > > RCX: 0000000000000000
> 
>   $ ./scripts/decodecode < oops
>     22:       53                      push   %rbx
>     23:       48 8b 5f 78             mov    0x78(%rdi),%rbx
>     27:       48 89 df                mov    %rbx,%rdi
>     2a:*      ff 93 40 05 00 00       callq  *0x540(%rbx)             <-- trapping instruction
>     30:       c6 83 c0 05 00 00 00    movb   $0x0,0x5c0(%rbx)
>     37:       5b                      pop    %rbx
>     38:       c3                      retq
> 
>   static int i2c_dw_pci_resume(struct device *dev)
>   {
>     struct dw_i2c_dev *i_dev = dev_get_drvdata(dev);
>     int ret;
> 
>     ret = i_dev->init(i_dev);
>     i_dev->suspended = false;
> 
>     return ret;
> 
> So I think we're trying to call i_dev->init(), which is a NULL
> pointer.
> 
> > > <4>[    1.431422][  T447]  pci_pm_runtime_resume+0xaa/0x100
> > > <4>[    1.431434][  T447]  __rpm_callback+0x3c/0x100
> > > <4>[    1.431442][  T447]  rpm_callback+0x54/0x80
> > > <4>[    1.431445][  T447]  rpm_resume+0x410/0x700
> > > <4>[    1.431455][  T447]  __pm_runtime_resume+0x45/0x80
> > > <4>[    1.431457][  T447]  pci_device_probe+0xa2/0x140
> > > <4>[    1.431459][  T447]  really_probe+0x1e4/0x400
> > > <4>[    1.431464][  T447]  __driver_probe_device+0xf9/0x180
> > > <4>[    1.431466][  T447]  driver_probe_device+0x19/0xc0
> 
> I think the problem here is that:
> 
>   - really_probe() sets dev->driver
> 
>   - local_pci_probe() calls pm_runtime_get_sync(), which leads to:
> 
>   - pci_pm_runtime_resume(), which previously skipped the driver's
>     .runtime_resume() method when "pci_dev->driver" as NULL
> 
>   - after 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of
>     pci_dev->driver") [1], it checks "dev->driver" instead of
>     "pci_dev->driver"
> 
>   - dev->driver is non-NULL (set by really_probe() above), but at this
>     point pci_dev->driver used to be NULL because local_pci_probe()
>     didn't set it until after after calling pm_runtime_get_sync() (see
>     b5f9c644eb1b ("PCI: Remove struct pci_dev->driver") [2])
> 
>   - because dev->driver is non-NULL, we call i2c_dw_pci_resume()
>     before i2c_dw_pci_probe(), so the driver init hasn't been done
> 
> Here's the call tree:
> 
>     really_probe
>       dev->driver = drv;                       # <--
>       call_driver_probe
>         dev->bus->probe
>           pci_device_probe
>             __pci_device_probe
>               pci_call_probe
>                 local_pci_probe
>                   pm_runtime_get_sync
>                     ...
>                     pci_pm_runtime_resume
>   -                   if (!pci_dev->driver)    # 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of pci_dev->driver")
>   +                   if (!to_pci_driver(dev->driver))
>                         return 0
>                       pm->runtime_resume
>                         i2c_dw_pci_resume
>                           i_dev->init()        # <-- NULL ptr deref
>   -                 pci_dev->driver = pci_drv  # b5f9c644eb1b ("PCI: Remove struct pci_dev->driver")
>                   pci_drv->probe
>                     i2c_dw_pci_probe
> 
> Note that we used to call pm_runtime_get_sync() (and the driver's
> runtime_resume() method) in the window where dev->driver had been set
> but pci_dev->driver had not.  Since we got rid of pci_dev->driver
> altogether, that window no longer exists, so we call the driver's
> runtime_resume() when it isn't prepared for it.
> 
> [1] https://git.kernel.org/linus/2a4d9408c9e8
> [2] https://git.kernel.org/linus/b5f9c644eb1b