Re: [PATCH] pci: Don't call resume callback for nearly bound devices

Bjorn Helgaas
2021-11-09T02:56:23Z

[+cc Greg: new device_is_bound() use]

On Mon, Nov 08, 2021 at 10:22:26PM +0100, Uwe Kleine-König wrote:
> pci_pm_runtime_resume() exits early when the device to resume isn't
> bound yet:
>
> if (!to_pci_driver(dev->driver))
> return 0;
>
> This however isn't true when the device currently probes and
> local_pci_probe() calls pm_runtime_get_sync() because then the driver
> core already setup dev->driver. As a result the driver's resume callback
> is called before the driver's probe function is called and so more often
> than not required driver data isn't setup yet.
>
> So replace the check for the device being unbound by a check that only
> becomes true after .probe() succeeded.

I like the fact that this patch is short and simple.

But there are 30+ users of to_pci_driver(). This patch asserts that
*one* of them, pci_pm_runtime_resume(), is special and needs to test
device_is_bound() instead of using to_pci_driver().

It's special because the current PM implementation calls it via
pm_runtime_get_sync() before the driver's .probe() method. That
connection is a little bit obscure and fragile. What if the PM
implementation changes?

Maybe we just need a comment there about why it looks different than
the other PM interfaces?

I also notice that the only other uses of device_is_bound()
outside the driver core are in iommu_group_store_type() and
regulator_resolve_supply(). This patch seems like a reasonable use,
but I always look twice when we do something unique.

> Reported-by: Robert Święcki <robert@swiecki.net>
> Fixes: 2a4d9408c9e8 ("PCI: Use to_pci_driver() instead of pci_dev->driver")
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
> On Mon, Nov 08, 2021 at 12:58:23PM -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
>
> I think this analysis is right.
>
> I didn't test this patch, @Robert, maybe you can do this?
>
> Best regards
> Uwe
>
> drivers/pci/pci-driver.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 1d98c974381c..202533654012 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -1299,7 +1299,7 @@ static int pci_pm_runtime_resume(struct device *dev)
> */
> pci_restore_standard_config(pci_dev);
>
> - if (!to_pci_driver(dev->driver))
> + if (!device_is_bound(dev))
> return 0;
>
> pci_fixup_device(pci_fixup_resume_early, pci_dev);
> --
> 2.30.2
>
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | https://www.pengutronix.de/ |