| Message ID | 20211217141709.379663-1-hdegoede@redhat.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
| Series | [resend,v2] PCI: pciehp: Use down_read/write_nested(reset_lock) to fix lockdep errors | expand |
On Fri, Dec 17, 2021 at 03:17:09PM +0100, Hans de Goede wrote: > Use down_read_nested() and down_write_nested() when taking the > ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in > the path to the PCI root bus as lock subclass parameter. This fixes the > following false-positive lockdep report when unplugging a Lenovo X1C8 from > a Lenovo 2nd gen TB3 dock: > > [ 28.583853] pcieport 0000:06:01.0: pciehp: Slot(1): Link Down > [ 28.583891] pcieport 0000:06:01.0: pciehp: Slot(1): Card not present > [ 28.584849] ============================================ > [ 28.584854] WARNING: possible recursive locking detected > [ 28.584858] 5.16.0-rc2+ #621 Not tainted > [ 28.584864] -------------------------------------------- > [ 28.584867] irq/124-pciehp/86 is trying to acquire lock: > [ 28.584873] ffff8e5ac4299ef8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_check_presence+0x23/0x80 > [ 28.584904] > but task is already holding lock: > [ 28.584908] ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180 > [ 28.584929] > other info that might help us debug this: > [ 28.584933] Possible unsafe locking scenario: > > [ 28.584936] CPU0 > [ 28.584939] ---- > [ 28.584942] lock(&ctrl->reset_lock); > [ 28.584949] lock(&ctrl->reset_lock); > [ 28.584955] > *** DEADLOCK *** > > [ 28.584959] May be due to missing lock nesting notation > > [ 28.584963] 3 locks held by irq/124-pciehp/86: > [ 28.584970] #0: ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180 > [ 28.584991] #1: ffffffffa3b024e8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: pciehp_unconfigure_device+0x31/0x110 > [ 28.585012] #2: ffff8e5ac1ee2248 (&dev->mutex){....}-{3:3}, at: device_release_driver+0x1c/0x40 > [ 28.585037] > stack backtrace: > [ 28.585042] CPU: 4 PID: 86 Comm: irq/124-pciehp Not tainted 5.16.0-rc2+ #621 > [ 28.585052] Hardware name: LENOVO 20U90SIT19/20U90SIT19, BIOS N2WET30W (1.20 ) 08/26/2021 > [ 28.585059] Call Trace: > [ 28.585064] <TASK> > [ 28.585073] dump_stack_lvl+0x59/0x73 > [ 28.585087] __lock_acquire.cold+0xc5/0x2c6 > [ 28.585106] ? find_held_lock+0x2b/0x80 > [ 28.585124] lock_acquire+0xb5/0x2b0 > [ 28.585132] ? pciehp_check_presence+0x23/0x80 > [ 28.585144] ? lock_is_held_type+0xa8/0x120 > [ 28.585161] down_read+0x3e/0x50 > [ 28.585172] ? pciehp_check_presence+0x23/0x80 > [ 28.585183] pciehp_check_presence+0x23/0x80 > [ 28.585194] pciehp_runtime_resume+0x5c/0xa0 > [ 28.585206] ? pci_msix_init+0x60/0x60 > [ 28.585214] device_for_each_child+0x45/0x70 > [ 28.585227] pcie_port_device_runtime_resume+0x20/0x30 > [ 28.585236] pci_pm_runtime_resume+0xa7/0xc0 > [ 28.585246] ? pci_pm_freeze_noirq+0x100/0x100 > [ 28.585257] __rpm_callback+0x41/0x110 > [ 28.585271] ? pci_pm_freeze_noirq+0x100/0x100 > [ 28.585281] rpm_callback+0x59/0x70 > [ 28.585293] rpm_resume+0x512/0x7b0 > [ 28.585309] __pm_runtime_resume+0x4a/0x90 > [ 28.585322] __device_release_driver+0x28/0x240 > [ 28.585338] device_release_driver+0x26/0x40 > [ 28.585351] pci_stop_bus_device+0x68/0x90 > [ 28.585363] pci_stop_bus_device+0x2c/0x90 > [ 28.585373] pci_stop_and_remove_bus_device+0xe/0x20 > [ 28.585384] pciehp_unconfigure_device+0x6c/0x110 > [ 28.585396] ? __pm_runtime_resume+0x58/0x90 > [ 28.585409] pciehp_disable_slot+0x5b/0xe0 > [ 28.585421] pciehp_handle_presence_or_link_change+0xc3/0x2f0 > [ 28.585436] pciehp_ist+0x179/0x180 > [ 28.585449] ? disable_irq_nosync+0x10/0x10 > [ 28.585460] irq_thread_fn+0x1d/0x60 > [ 28.585470] ? irq_thread+0x81/0x1a0 > [ 28.585480] irq_thread+0xcb/0x1a0 > [ 28.585491] ? irq_thread_fn+0x60/0x60 > [ 28.585502] ? irq_thread_check_affinity+0xb0/0xb0 > [ 28.585514] kthread+0x165/0x190 > [ 28.585522] ? set_kthread_struct+0x40/0x40 > [ 28.585531] ret_from_fork+0x1f/0x30 > [ 28.585554] </TASK> > > This lockdep warning is triggered because with Thunderbolt, hotplug ports > are nested. When removing multiple devices in a daisy-chain, each hotplug > port's reset_lock may be acquired recursively. It's never the same lock, > so the lockdep splat is a false positive. > > Because locks at the same hierarchy level are never acquired recursively, > a per-level lockdep class is sufficient to fix the lockdep warning. > > The choice to use one lockdep subclass per pcie-hotplug controller in > the path to the root-bus was made to conserve class keys because their > number is limited and the complexity grows quadratically with number of > keys according to Documentation/locking/lockdep-design.rst. > > Link: https://lore.kernel.org/linux-pci/20190402021933.GA2966@mit.edu/ > Link: https://lore.kernel.org/linux-pci/de684a28-9038-8fc6-27ca-3f6f2f6400d7@redhat.com/ > Cc: stable@vger.kernel.org > Reported-by: "Theodore Ts'o" <tytso@mit.edu> > Reviewed-by: Lukas Wunner <lukas@wunner.de> > Signed-off-by: Hans de Goede <hdegoede@redhat.com> Applied to pci/hotplug for v5.17, thanks, Hans! > --- > Changes in v2: > - Only use a subclass for each hotplug capable port/parent in the path to > the PCI root bus, instead of one for each level in the PCI hierarchy, > to avoid hitting MAX_LOCKDEP_SUBCLASSES > - Drop the "PCI: Add a pci_dev_depth() helper function" since we now need > a special version of this to only count hotplug ports > - Various commit message improvements > --- > drivers/pci/hotplug/pciehp.h | 3 +++ > drivers/pci/hotplug/pciehp_core.c | 2 +- > drivers/pci/hotplug/pciehp_hpc.c | 21 ++++++++++++++++++--- > 3 files changed, 22 insertions(+), 4 deletions(-) > > diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h > index 918dccbc74b6..e0a614acee05 100644 > --- a/drivers/pci/hotplug/pciehp.h > +++ b/drivers/pci/hotplug/pciehp.h > @@ -75,6 +75,8 @@ extern int pciehp_poll_time; > * @reset_lock: prevents access to the Data Link Layer Link Active bit in the > * Link Status register and to the Presence Detect State bit in the Slot > * Status register during a slot reset which may cause them to flap > + * @depth: Number of additional hotplug ports in the path to the root bus, > + * used as lock subclass for @reset_lock > * @ist_running: flag to keep user request waiting while IRQ thread is running > * @request_result: result of last user request submitted to the IRQ thread > * @requester: wait queue to wake up on completion of user request, > @@ -106,6 +108,7 @@ struct controller { > > struct hotplug_slot hotplug_slot; /* hotplug core interface */ > struct rw_semaphore reset_lock; > + unsigned int depth; > unsigned int ist_running; > int request_result; > wait_queue_head_t requester; > diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c > index f34114d45259..4042d87d539d 100644 > --- a/drivers/pci/hotplug/pciehp_core.c > +++ b/drivers/pci/hotplug/pciehp_core.c > @@ -166,7 +166,7 @@ static void pciehp_check_presence(struct controller *ctrl) > { > int occupied; > > - down_read(&ctrl->reset_lock); > + down_read_nested(&ctrl->reset_lock, ctrl->depth); > mutex_lock(&ctrl->state_lock); > > occupied = pciehp_card_present_or_link_active(ctrl); > diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c > index 83a0fa119cae..963fb50528da 100644 > --- a/drivers/pci/hotplug/pciehp_hpc.c > +++ b/drivers/pci/hotplug/pciehp_hpc.c > @@ -583,7 +583,7 @@ static void pciehp_ignore_dpc_link_change(struct controller *ctrl, > * the corresponding link change may have been ignored above. > * Synthesize it to ensure that it is acted on. > */ > - down_read(&ctrl->reset_lock); > + down_read_nested(&ctrl->reset_lock, ctrl->depth); > if (!pciehp_check_link_active(ctrl)) > pciehp_request(ctrl, PCI_EXP_SLTSTA_DLLSC); > up_read(&ctrl->reset_lock); > @@ -746,7 +746,7 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) > * Disable requests have higher priority than Presence Detect Changed > * or Data Link Layer State Changed events. > */ > - down_read(&ctrl->reset_lock); > + down_read_nested(&ctrl->reset_lock, ctrl->depth); > if (events & DISABLE_SLOT) > pciehp_handle_disable_request(ctrl); > else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) > @@ -906,7 +906,7 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, bool probe) > if (probe) > return 0; > > - down_write(&ctrl->reset_lock); > + down_write_nested(&ctrl->reset_lock, ctrl->depth); > > if (!ATTN_BUTTN(ctrl)) { > ctrl_mask |= PCI_EXP_SLTCTL_PDCE; > @@ -962,6 +962,20 @@ static inline void dbg_ctrl(struct controller *ctrl) > > #define FLAG(x, y) (((x) & (y)) ? '+' : '-') > > +static inline int pcie_hotplug_depth(struct pci_dev *dev) > +{ > + struct pci_bus *bus = dev->bus; > + int depth = 0; > + > + while (bus->parent) { > + bus = bus->parent; > + if (bus->self && bus->self->is_hotplug_bridge) > + depth++; > + } > + > + return depth; > +} > + > struct controller *pcie_init(struct pcie_device *dev) > { > struct controller *ctrl; > @@ -975,6 +989,7 @@ struct controller *pcie_init(struct pcie_device *dev) > return NULL; > > ctrl->pcie = dev; > + ctrl->depth = pcie_hotplug_depth(dev->port); > pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &slot_cap); > > if (pdev->hotplug_user_indicators) > -- > 2.33.1 >
On Tue, Jan 11, 2022 at 11:14:47AM -0600, Bjorn Helgaas wrote: > On Fri, Dec 17, 2021 at 03:17:09PM +0100, Hans de Goede wrote: > > Use down_read_nested() and down_write_nested() when taking the > > ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in > > the path to the PCI root bus as lock subclass parameter. This fixes the > > following false-positive lockdep report when unplugging a Lenovo X1C8 from > > a Lenovo 2nd gen TB3 dock: [...] > Applied to pci/hotplug for v5.17, thanks, Hans! I've realized only now that Hans reported this issue already in August 2020 and opened a bugzilla for it: https://bugzilla.kernel.org/show_bug.cgi?id=208855 The status can now be set to RESOLVED FIXED. I don't have permission to do that but perhaps either of you, Bjorn or Hans, has? Also, the commit could optionally be amended with a Link: tag to that bugzilla entry. Thanks, Lukas
Hi, On 1/12/22 09:28, Lukas Wunner wrote: > On Tue, Jan 11, 2022 at 11:14:47AM -0600, Bjorn Helgaas wrote: >> On Fri, Dec 17, 2021 at 03:17:09PM +0100, Hans de Goede wrote: >>> Use down_read_nested() and down_write_nested() when taking the >>> ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in >>> the path to the PCI root bus as lock subclass parameter. This fixes the >>> following false-positive lockdep report when unplugging a Lenovo X1C8 from >>> a Lenovo 2nd gen TB3 dock: > [...] >> Applied to pci/hotplug for v5.17, thanks, Hans! > > I've realized only now that Hans reported this issue already in August 2020 > and opened a bugzilla for it: > > https://bugzilla.kernel.org/show_bug.cgi?id=208855 Ah I completely forgot about having filed that bug, good catch. > The status can now be set to RESOLVED FIXED. I don't have permission > to do that but perhaps either of you, Bjorn or Hans, has? I have added a comment and closed the bug now. Note that you can email the kernel.org admins with your bugzilla login + a friendly requests to give you some more bugzilla rights. I did that a while ago when I hit similar issues doing triage of bugzilla.kernel.org bugs. > Also, the commit could optionally be amended with a Link: tag to that > bugzilla entry. There isn't really any new info in the bugzilla though, so I guess the commit is fine as is. With that said if Bjorn wants to add it that is fine too of course. Regards, Hans
On Wed, Jan 12, 2022 at 01:39:07PM +0100, Hans de Goede wrote: > Hi, > > On 1/12/22 09:28, Lukas Wunner wrote: > > On Tue, Jan 11, 2022 at 11:14:47AM -0600, Bjorn Helgaas wrote: > >> On Fri, Dec 17, 2021 at 03:17:09PM +0100, Hans de Goede wrote: > >>> Use down_read_nested() and down_write_nested() when taking the > >>> ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in > >>> the path to the PCI root bus as lock subclass parameter. This fixes the > >>> following false-positive lockdep report when unplugging a Lenovo X1C8 from > >>> a Lenovo 2nd gen TB3 dock: > > [...] > >> Applied to pci/hotplug for v5.17, thanks, Hans! > > > > I've realized only now that Hans reported this issue already in August 2020 > > and opened a bugzilla for it: > > > > https://bugzilla.kernel.org/show_bug.cgi?id=208855 > > Ah I completely forgot about having filed that bug, good catch. > > > The status can now be set to RESOLVED FIXED. I don't have permission > > to do that but perhaps either of you, Bjorn or Hans, has? > > I have added a comment and closed the bug now. Note that you can email > the kernel.org admins with your bugzilla login + a friendly requests > to give you some more bugzilla rights. I did that a while ago when > I hit similar issues doing triage of bugzilla.kernel.org bugs. > > > Also, the commit could optionally be amended with a Link: tag to that > > bugzilla entry. > > There isn't really any new info in the bugzilla though, so I guess > the commit is fine as is. With that said if Bjorn wants to add it > that is fine too of course. Thanks, I added it. It does have a link to Ted's original email, which includes a complete dmesg log. Of course, that makes the commit referenced by https://bugzilla.kernel.org/show_bug.cgi?id=208855#c2 obsolete, but that happens anyway because I often rebase to add things like this. Bjorn
diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h index 918dccbc74b6..e0a614acee05 100644 --- a/drivers/pci/hotplug/pciehp.h +++ b/drivers/pci/hotplug/pciehp.h @@ -75,6 +75,8 @@ extern int pciehp_poll_time; * @reset_lock: prevents access to the Data Link Layer Link Active bit in the * Link Status register and to the Presence Detect State bit in the Slot * Status register during a slot reset which may cause them to flap + * @depth: Number of additional hotplug ports in the path to the root bus, + * used as lock subclass for @reset_lock * @ist_running: flag to keep user request waiting while IRQ thread is running * @request_result: result of last user request submitted to the IRQ thread * @requester: wait queue to wake up on completion of user request, @@ -106,6 +108,7 @@ struct controller { struct hotplug_slot hotplug_slot; /* hotplug core interface */ struct rw_semaphore reset_lock; + unsigned int depth; unsigned int ist_running; int request_result; wait_queue_head_t requester; diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c index f34114d45259..4042d87d539d 100644 --- a/drivers/pci/hotplug/pciehp_core.c +++ b/drivers/pci/hotplug/pciehp_core.c @@ -166,7 +166,7 @@ static void pciehp_check_presence(struct controller *ctrl) { int occupied; - down_read(&ctrl->reset_lock); + down_read_nested(&ctrl->reset_lock, ctrl->depth); mutex_lock(&ctrl->state_lock); occupied = pciehp_card_present_or_link_active(ctrl); diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c index 83a0fa119cae..963fb50528da 100644 --- a/drivers/pci/hotplug/pciehp_hpc.c +++ b/drivers/pci/hotplug/pciehp_hpc.c @@ -583,7 +583,7 @@ static void pciehp_ignore_dpc_link_change(struct controller *ctrl, * the corresponding link change may have been ignored above. * Synthesize it to ensure that it is acted on. */ - down_read(&ctrl->reset_lock); + down_read_nested(&ctrl->reset_lock, ctrl->depth); if (!pciehp_check_link_active(ctrl)) pciehp_request(ctrl, PCI_EXP_SLTSTA_DLLSC); up_read(&ctrl->reset_lock); @@ -746,7 +746,7 @@ static irqreturn_t pciehp_ist(int irq, void *dev_id) * Disable requests have higher priority than Presence Detect Changed * or Data Link Layer State Changed events. */ - down_read(&ctrl->reset_lock); + down_read_nested(&ctrl->reset_lock, ctrl->depth); if (events & DISABLE_SLOT) pciehp_handle_disable_request(ctrl); else if (events & (PCI_EXP_SLTSTA_PDC | PCI_EXP_SLTSTA_DLLSC)) @@ -906,7 +906,7 @@ int pciehp_reset_slot(struct hotplug_slot *hotplug_slot, bool probe) if (probe) return 0; - down_write(&ctrl->reset_lock); + down_write_nested(&ctrl->reset_lock, ctrl->depth); if (!ATTN_BUTTN(ctrl)) { ctrl_mask |= PCI_EXP_SLTCTL_PDCE; @@ -962,6 +962,20 @@ static inline void dbg_ctrl(struct controller *ctrl) #define FLAG(x, y) (((x) & (y)) ? '+' : '-') +static inline int pcie_hotplug_depth(struct pci_dev *dev) +{ + struct pci_bus *bus = dev->bus; + int depth = 0; + + while (bus->parent) { + bus = bus->parent; + if (bus->self && bus->self->is_hotplug_bridge) + depth++; + } + + return depth; +} + struct controller *pcie_init(struct pcie_device *dev) { struct controller *ctrl; @@ -975,6 +989,7 @@ struct controller *pcie_init(struct pcie_device *dev) return NULL; ctrl->pcie = dev; + ctrl->depth = pcie_hotplug_depth(dev->port); pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &slot_cap); if (pdev->hotplug_user_indicators)
Use down_read_nested() and down_write_nested() when taking the ctrl->reset_lock rw-sem, passing the number of PCIe hotplug controllers in the path to the PCI root bus as lock subclass parameter. This fixes the following false-positive lockdep report when unplugging a Lenovo X1C8 from a Lenovo 2nd gen TB3 dock: [ 28.583853] pcieport 0000:06:01.0: pciehp: Slot(1): Link Down [ 28.583891] pcieport 0000:06:01.0: pciehp: Slot(1): Card not present [ 28.584849] ============================================ [ 28.584854] WARNING: possible recursive locking detected [ 28.584858] 5.16.0-rc2+ #621 Not tainted [ 28.584864] -------------------------------------------- [ 28.584867] irq/124-pciehp/86 is trying to acquire lock: [ 28.584873] ffff8e5ac4299ef8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_check_presence+0x23/0x80 [ 28.584904] but task is already holding lock: [ 28.584908] ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180 [ 28.584929] other info that might help us debug this: [ 28.584933] Possible unsafe locking scenario: [ 28.584936] CPU0 [ 28.584939] ---- [ 28.584942] lock(&ctrl->reset_lock); [ 28.584949] lock(&ctrl->reset_lock); [ 28.584955] *** DEADLOCK *** [ 28.584959] May be due to missing lock nesting notation [ 28.584963] 3 locks held by irq/124-pciehp/86: [ 28.584970] #0: ffff8e5ac4298af8 (&ctrl->reset_lock){.+.+}-{3:3}, at: pciehp_ist+0xf3/0x180 [ 28.584991] #1: ffffffffa3b024e8 (pci_rescan_remove_lock){+.+.}-{3:3}, at: pciehp_unconfigure_device+0x31/0x110 [ 28.585012] #2: ffff8e5ac1ee2248 (&dev->mutex){....}-{3:3}, at: device_release_driver+0x1c/0x40 [ 28.585037] stack backtrace: [ 28.585042] CPU: 4 PID: 86 Comm: irq/124-pciehp Not tainted 5.16.0-rc2+ #621 [ 28.585052] Hardware name: LENOVO 20U90SIT19/20U90SIT19, BIOS N2WET30W (1.20 ) 08/26/2021 [ 28.585059] Call Trace: [ 28.585064] <TASK> [ 28.585073] dump_stack_lvl+0x59/0x73 [ 28.585087] __lock_acquire.cold+0xc5/0x2c6 [ 28.585106] ? find_held_lock+0x2b/0x80 [ 28.585124] lock_acquire+0xb5/0x2b0 [ 28.585132] ? pciehp_check_presence+0x23/0x80 [ 28.585144] ? lock_is_held_type+0xa8/0x120 [ 28.585161] down_read+0x3e/0x50 [ 28.585172] ? pciehp_check_presence+0x23/0x80 [ 28.585183] pciehp_check_presence+0x23/0x80 [ 28.585194] pciehp_runtime_resume+0x5c/0xa0 [ 28.585206] ? pci_msix_init+0x60/0x60 [ 28.585214] device_for_each_child+0x45/0x70 [ 28.585227] pcie_port_device_runtime_resume+0x20/0x30 [ 28.585236] pci_pm_runtime_resume+0xa7/0xc0 [ 28.585246] ? pci_pm_freeze_noirq+0x100/0x100 [ 28.585257] __rpm_callback+0x41/0x110 [ 28.585271] ? pci_pm_freeze_noirq+0x100/0x100 [ 28.585281] rpm_callback+0x59/0x70 [ 28.585293] rpm_resume+0x512/0x7b0 [ 28.585309] __pm_runtime_resume+0x4a/0x90 [ 28.585322] __device_release_driver+0x28/0x240 [ 28.585338] device_release_driver+0x26/0x40 [ 28.585351] pci_stop_bus_device+0x68/0x90 [ 28.585363] pci_stop_bus_device+0x2c/0x90 [ 28.585373] pci_stop_and_remove_bus_device+0xe/0x20 [ 28.585384] pciehp_unconfigure_device+0x6c/0x110 [ 28.585396] ? __pm_runtime_resume+0x58/0x90 [ 28.585409] pciehp_disable_slot+0x5b/0xe0 [ 28.585421] pciehp_handle_presence_or_link_change+0xc3/0x2f0 [ 28.585436] pciehp_ist+0x179/0x180 [ 28.585449] ? disable_irq_nosync+0x10/0x10 [ 28.585460] irq_thread_fn+0x1d/0x60 [ 28.585470] ? irq_thread+0x81/0x1a0 [ 28.585480] irq_thread+0xcb/0x1a0 [ 28.585491] ? irq_thread_fn+0x60/0x60 [ 28.585502] ? irq_thread_check_affinity+0xb0/0xb0 [ 28.585514] kthread+0x165/0x190 [ 28.585522] ? set_kthread_struct+0x40/0x40 [ 28.585531] ret_from_fork+0x1f/0x30 [ 28.585554] </TASK> This lockdep warning is triggered because with Thunderbolt, hotplug ports are nested. When removing multiple devices in a daisy-chain, each hotplug port's reset_lock may be acquired recursively. It's never the same lock, so the lockdep splat is a false positive. Because locks at the same hierarchy level are never acquired recursively, a per-level lockdep class is sufficient to fix the lockdep warning. The choice to use one lockdep subclass per pcie-hotplug controller in the path to the root-bus was made to conserve class keys because their number is limited and the complexity grows quadratically with number of keys according to Documentation/locking/lockdep-design.rst. Link: https://lore.kernel.org/linux-pci/20190402021933.GA2966@mit.edu/ Link: https://lore.kernel.org/linux-pci/de684a28-9038-8fc6-27ca-3f6f2f6400d7@redhat.com/ Cc: stable@vger.kernel.org Reported-by: "Theodore Ts'o" <tytso@mit.edu> Reviewed-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Hans de Goede <hdegoede@redhat.com> --- Changes in v2: - Only use a subclass for each hotplug capable port/parent in the path to the PCI root bus, instead of one for each level in the PCI hierarchy, to avoid hitting MAX_LOCKDEP_SUBCLASSES - Drop the "PCI: Add a pci_dev_depth() helper function" since we now need a special version of this to only count hotplug ports - Various commit message improvements --- drivers/pci/hotplug/pciehp.h | 3 +++ drivers/pci/hotplug/pciehp_core.c | 2 +- drivers/pci/hotplug/pciehp_hpc.c | 21 ++++++++++++++++++--- 3 files changed, 22 insertions(+), 4 deletions(-)