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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Mon, 4 Mar 2024 18:00:41 +0100
Message-ID: <CAJZ5v0idOkeod9-RmnNGCwMGG+9nYi8eJSBpQYWJnv=N+eVoWg@mail.gmail.com>
Subject: Re: [PATCH v3] driver core: Cancel scheduled pm_runtime_idle() on
 device removal
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>, gregkh@linuxfoundation.org, 
	bhelgaas@google.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, 
	Ricky Wu <ricky_wu@realtek.com>, Kees Cook <keescook@chromium.org>, 
	Tony Luck <tony.luck@intel.com>, "Guilherme G. Piccoli" <gpiccoli@igalia.com>, 
	linux-hardening@vger.kernel.org, bpf@vger.kernel.org
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On Mon, Mar 4, 2024 at 5:41=E2=80=AFPM Rafael J. Wysocki <rafael@kernel.org=
> wrote:
>
> On Mon, Mar 4, 2024 at 4:51=E2=80=AFPM Bjorn Helgaas <helgaas@kernel.org>=
 wrote:
> >
> > On Mon, Mar 04, 2024 at 03:38:38PM +0100, Rafael J. Wysocki wrote:
> > > On Thu, Feb 29, 2024 at 7:23=E2=80=AFAM Kai-Heng Feng
> > > <kai.heng.feng@canonical.com> wrote:
> > > >
> > > > When inserting an SD7.0 card to Realtek card reader, the card reade=
r
> > > > unplugs itself and morph into a NVMe device. The slot Link down on =
hot
> > > > unplugged can cause the following error:
> > > >
> > > > pcieport 0000:00:1c.0: pciehp: Slot(8): Link Down
> > > > BUG: unable to handle page fault for address: ffffb24d403e5010
> > > > PGD 100000067 P4D 100000067 PUD 1001fe067 PMD 100d97067 PTE 0
> > > > Oops: 0000 [#1] PREEMPT SMP PTI
> > > > CPU: 3 PID: 534 Comm: kworker/3:10 Not tainted 6.4.0 #6
> > > > Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./H370M =
Pro4, BIOS P3.40 10/25/2018
> > > > Workqueue: pm pm_runtime_work
> > > > RIP: 0010:ioread32+0x2e/0x70
> > > ...
> > > > Call Trace:
> > > >  <TASK>
> > > >  ? show_regs+0x68/0x70
> > > >  ? __die_body+0x20/0x70
> > > >  ? __die+0x2b/0x40
> > > >  ? page_fault_oops+0x160/0x480
> > > >  ? search_bpf_extables+0x63/0x90
> > > >  ? ioread32+0x2e/0x70
> > > >  ? search_exception_tables+0x5f/0x70
> > > >  ? kernelmode_fixup_or_oops+0xa2/0x120
> > > >  ? __bad_area_nosemaphore+0x179/0x230
> > > >  ? bad_area_nosemaphore+0x16/0x20
> > > >  ? do_kern_addr_fault+0x8b/0xa0
> > > >  ? exc_page_fault+0xe5/0x180
> > > >  ? asm_exc_page_fault+0x27/0x30
> > > >  ? ioread32+0x2e/0x70
> > > >  ? rtsx_pci_write_register+0x5b/0x90 [rtsx_pci]
> > > >  rtsx_set_l1off_sub+0x1c/0x30 [rtsx_pci]
> > > >  rts5261_set_l1off_cfg_sub_d0+0x36/0x40 [rtsx_pci]
> > > >  rtsx_pci_runtime_idle+0xc7/0x160 [rtsx_pci]
> > > >  ? __pfx_pci_pm_runtime_idle+0x10/0x10
> > > >  pci_pm_runtime_idle+0x34/0x70
> > > >  rpm_idle+0xc4/0x2b0
> > > >  pm_runtime_work+0x93/0xc0
> > > >  process_one_work+0x21a/0x430
> > > >  worker_thread+0x4a/0x3c0
> > > ...
> >
> > > > This happens because scheduled pm_runtime_idle() is not cancelled.
> > >
> > > But rpm_resume() changes dev->power.request to RPM_REQ_NONE and if
> > > pm_runtime_work() sees this, it will not run rpm_idle().
> > >
> > > However, rpm_resume() doesn't deactivate the autosuspend timer if it
> > > is running (see the comment in rpm_resume() regarding this), so it ma=
y
> > > queue up a runtime PM work later.
> > >
> > > If this is not desirable, you need to stop the autosuspend timer
> > > explicitly in addition to calling pm_runtime_get_sync().
> >
> > I don't quite follow all this.  I think the race is between
> > rtsx_pci_remove() (not resume) and rtsx_pci_runtime_idle().
>
> I think so too and the latter is not expected to run.
>
> >   rtsx_pci_remove()
> >   {
> >     pm_runtime_get_sync()
> >     pm_runtime_forbid()
> >     ...
> >
> > If this is an rtsx bug, what exactly should be added to
> > rtsx_pci_remove()?
> >
> > Is there ever a case where we want any runtime PM work to happen
> > during or after a driver .remove()?  If not, maybe the driver core
> > should prevent that, which I think is basically what this patch does.
>
> No, it is not, because it doesn't actually prevent the race from
> occurring, it just narrows the window quite a bit.
>
> It would be better to call pm_runtime_dont_use_autosuspend() instead
> of pm_runtime_barrier().
>
> > If this is an rtsx driver bug, I'm concerned there may be many other
> > drivers with a similar issue.  rtsx exercises this path more than most
> > because the device switches between card reader and NVMe SSD using
> > hotplug add/remove based on whether an SD card is inserted (see [1]).
>
> This is a valid concern, so it is mostly a matter of where to disable
> autosuspend.
>
> It may be the driver core in principle, but note that it calls
> ->remove() after invoking pm_runtime_put_sync(), so why would it
> disable autosuspend when it allows runtime PM to race with device
> removal in general?
>
> Another way might be to add a pm_runtime_dont_use_autosuspend() call
> at the beginning of pci_device_remove().
>
> Or just remove the optimization in question from rpm_resume() which is
> quite confusing and causes people to make assumptions that lead to
> incorrect behavior in this particular case.

Well, scratch this.

If rpm_idle() is already running at the time rpm_resume() is called,
the latter may return right away without waiting, which is incorrect.

rpm_resume() needs to wait for the "idle" callback to complete, so
this (again, modulo GMail-induced whitespace mangling) should help:

---
 drivers/base/power/runtime.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-pm/drivers/base/power/runtime.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
--- linux-pm.orig/drivers/base/power/runtime.c
+++ linux-pm/drivers/base/power/runtime.c
@@ -798,7 +798,8 @@ static int rpm_resume(struct device *dev
     }

     if (dev->power.runtime_status =3D=3D RPM_RESUMING ||
-        dev->power.runtime_status =3D=3D RPM_SUSPENDING) {
+        dev->power.runtime_status =3D=3D RPM_SUSPENDING ||
+        dev->power.idle_notification) {
         DEFINE_WAIT(wait);

         if (rpmflags & (RPM_ASYNC | RPM_NOWAIT)) {
@@ -826,7 +827,8 @@ static int rpm_resume(struct device *dev
             prepare_to_wait(&dev->power.wait_queue, &wait,
                     TASK_UNINTERRUPTIBLE);
             if (dev->power.runtime_status !=3D RPM_RESUMING &&
-                dev->power.runtime_status !=3D RPM_SUSPENDING)
+                dev->power.runtime_status !=3D RPM_SUSPENDING &&
+                !dev->power.idle_notification)
                 break;

             spin_unlock_irq(&dev->power.lock);