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Message-ID: <CAJZ5v0idOkeod9-RmnNGCwMGG+9nYi8eJSBpQYWJnv=N+eVoWg@mail.gmail.com>
Date: Mon, 4 Mar 2024 18:00:41 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Kai-Heng Feng <kai.heng.feng@...onical.com>, gregkh@...uxfoundation.org,
bhelgaas@...gle.com, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
Ricky Wu <ricky_wu@...ltek.com>, Kees Cook <keescook@...omium.org>,
Tony Luck <tony.luck@...el.com>, "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
linux-hardening@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v3] driver core: Cancel scheduled pm_runtime_idle() on
device removal
On Mon, Mar 4, 2024 at 5:41 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Mon, Mar 4, 2024 at 4:51 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> >
> > On Mon, Mar 04, 2024 at 03:38:38PM +0100, Rafael J. Wysocki wrote:
> > > On Thu, Feb 29, 2024 at 7:23 AM Kai-Heng Feng
> > > <kai.heng.feng@...onical.com> wrote:
> > > >
> > > > When inserting an SD7.0 card to Realtek card reader, the card reader
> > > > 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 may
> > > 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
===================================================================
--- 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 == RPM_RESUMING ||
- dev->power.runtime_status == RPM_SUSPENDING) {
+ dev->power.runtime_status == 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 != RPM_RESUMING &&
- dev->power.runtime_status != RPM_SUSPENDING)
+ dev->power.runtime_status != RPM_SUSPENDING &&
+ !dev->power.idle_notification)
break;
spin_unlock_irq(&dev->power.lock);
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