| Message ID | 20231128081512.19387-2-johan+linaro@kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | PCI: Fix deadlocks when enabling ASPM | expand |
[+cc Kai-Heng] On Tue, Nov 28, 2023 at 09:15:07AM +0100, Johan Hovold wrote: > Add a helper for enabling link states that can be used in contexts where > a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()). > > This helper will be used to fix a couple of potential deadlocks where > the current helper is called with the lock already held, hence the CC > stable tag. > > Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR") > Cc: stable@vger.kernel.org # 6.3 > Cc: Michael Bottini <michael.a.bottini@linux.intel.com> > Cc: David E. Box <david.e.box@linux.intel.com> > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > Signed-off-by: Johan Hovold <johan+linaro@kernel.org> > --- > drivers/pci/pcie/aspm.c | 53 +++++++++++++++++++++++++++++++---------- > include/linux/pci.h | 3 +++ > 2 files changed, 43 insertions(+), 13 deletions(-) > > diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c > index 50b04ae5c394..5eb462772354 100644 > --- a/drivers/pci/pcie/aspm.c > +++ b/drivers/pci/pcie/aspm.c > @@ -1109,17 +1109,7 @@ int pci_disable_link_state(struct pci_dev *pdev, int state) > } > EXPORT_SYMBOL(pci_disable_link_state); > > -/** > - * pci_enable_link_state - Clear and set the default device link state so that > - * the link may be allowed to enter the specified states. Note that if the > - * BIOS didn't grant ASPM control to the OS, this does nothing because we can't > - * touch the LNKCTL register. Also note that this does not enable states > - * disabled by pci_disable_link_state(). Return 0 or a negative errno. > - * > - * @pdev: PCI device > - * @state: Mask of ASPM link states to enable > - */ > -int pci_enable_link_state(struct pci_dev *pdev, int state) > +static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked) > { > struct pcie_link_state *link = pcie_aspm_get_link(pdev); > > @@ -1136,7 +1126,8 @@ int pci_enable_link_state(struct pci_dev *pdev, int state) > return -EPERM; > } > > - down_read(&pci_bus_sem); > + if (!locked) > + down_read(&pci_bus_sem); > mutex_lock(&aspm_lock); > link->aspm_default = 0; > if (state & PCIE_LINK_STATE_L0S) > @@ -1157,12 +1148,48 @@ int pci_enable_link_state(struct pci_dev *pdev, int state) > link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0; > pcie_set_clkpm(link, policy_to_clkpm_state(link)); > mutex_unlock(&aspm_lock); > - up_read(&pci_bus_sem); > + if (!locked) > + up_read(&pci_bus_sem); > > return 0; > } > + > +/** > + * pci_enable_link_state - Clear and set the default device link state so that > + * the link may be allowed to enter the specified states. Note that if the > + * BIOS didn't grant ASPM control to the OS, this does nothing because we can't > + * touch the LNKCTL register. Also note that this does not enable states > + * disabled by pci_disable_link_state(). Return 0 or a negative errno. > + * > + * @pdev: PCI device > + * @state: Mask of ASPM link states to enable > + */ > +int pci_enable_link_state(struct pci_dev *pdev, int state) > +{ > + return __pci_enable_link_state(pdev, state, false); > +} > EXPORT_SYMBOL(pci_enable_link_state); As far as I can see, we end up with pci_enable_link_state() defined but never called and pci_enable_link_state_locked() being called only by pcie-qcom.c and vmd.c. Can we just rename pci_enable_link_state() to pci_enable_link_state_locked() and assert that pci_bus_sem is held, so we don't end up with a function that's never used? I hope we can obsolete this whole idea someday. Using pci_walk_bus() in qcom and vmd to enable ASPM is an ugly hack to work around this weird idea that "the OS isn't allowed to enable more ASPM states than the BIOS did because the BIOS might have left ASPM disabled because it knows about hardware issues." More history at https://lore.kernel.org/linux-pci/20230615070421.1704133-1-kai.heng.feng@canonical.com/T/#u I think we need to get to a point where Linux enables all supported ASPM features by default. If we really think x86 BIOS assumes an implicit contract that the OS will never enable ASPM more aggressively, we might need some kind of arch quirk for that. If we can get there, the qcom use of pci_enable_link_state() could go away, and the vmd use could be replaced by some kind of "if device is below VMD, get rid of the legacy x86 ASPM assumption" quirk. Bjorn
On Thu, Dec 07, 2023 at 02:47:16PM -0600, Bjorn Helgaas wrote: > [+cc Kai-Heng] > > On Tue, Nov 28, 2023 at 09:15:07AM +0100, Johan Hovold wrote: > > Add a helper for enabling link states that can be used in contexts where > > a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()). > > > > This helper will be used to fix a couple of potential deadlocks where > > the current helper is called with the lock already held, hence the CC > > stable tag. > As far as I can see, we end up with pci_enable_link_state() defined > but never called and pci_enable_link_state_locked() being called only > by pcie-qcom.c and vmd.c. Correct, I mentioned this in the cover letter. > Can we just rename pci_enable_link_state() to > pci_enable_link_state_locked() and assert that pci_bus_sem is held, so > we don't end up with a function that's never used? That would work too. I went with adding a new helper to facilitate stable backports and to mirror pci_disable_link_state(). The variants are simple wrappers around the implementation so there's no real cost to having the unused one. But it seems like you think there will never be a need to call this helper outside of pci_walk_bus() and if so we can drop the unlocked variant right away. Would you prefer basically squashing the first three patches and mark the result for stable even though that patch will fail to apply to older kernels as the Qualcomm bits went into -rc1? Or should I send a follow-on patch removing the unused helper after merging this series? The end-result will be identical. Johan
diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c index 50b04ae5c394..5eb462772354 100644 --- a/drivers/pci/pcie/aspm.c +++ b/drivers/pci/pcie/aspm.c @@ -1109,17 +1109,7 @@ int pci_disable_link_state(struct pci_dev *pdev, int state) } EXPORT_SYMBOL(pci_disable_link_state); -/** - * pci_enable_link_state - Clear and set the default device link state so that - * the link may be allowed to enter the specified states. Note that if the - * BIOS didn't grant ASPM control to the OS, this does nothing because we can't - * touch the LNKCTL register. Also note that this does not enable states - * disabled by pci_disable_link_state(). Return 0 or a negative errno. - * - * @pdev: PCI device - * @state: Mask of ASPM link states to enable - */ -int pci_enable_link_state(struct pci_dev *pdev, int state) +static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked) { struct pcie_link_state *link = pcie_aspm_get_link(pdev); @@ -1136,7 +1126,8 @@ int pci_enable_link_state(struct pci_dev *pdev, int state) return -EPERM; } - down_read(&pci_bus_sem); + if (!locked) + down_read(&pci_bus_sem); mutex_lock(&aspm_lock); link->aspm_default = 0; if (state & PCIE_LINK_STATE_L0S) @@ -1157,12 +1148,48 @@ int pci_enable_link_state(struct pci_dev *pdev, int state) link->clkpm_default = (state & PCIE_LINK_STATE_CLKPM) ? 1 : 0; pcie_set_clkpm(link, policy_to_clkpm_state(link)); mutex_unlock(&aspm_lock); - up_read(&pci_bus_sem); + if (!locked) + up_read(&pci_bus_sem); return 0; } + +/** + * pci_enable_link_state - Clear and set the default device link state so that + * the link may be allowed to enter the specified states. Note that if the + * BIOS didn't grant ASPM control to the OS, this does nothing because we can't + * touch the LNKCTL register. Also note that this does not enable states + * disabled by pci_disable_link_state(). Return 0 or a negative errno. + * + * @pdev: PCI device + * @state: Mask of ASPM link states to enable + */ +int pci_enable_link_state(struct pci_dev *pdev, int state) +{ + return __pci_enable_link_state(pdev, state, false); +} EXPORT_SYMBOL(pci_enable_link_state); +/** + * pci_enable_link_state_locked - Clear and set the default device link state + * so that the link may be allowed to enter the specified states. Note that if + * the BIOS didn't grant ASPM control to the OS, this does nothing because we + * can't touch the LNKCTL register. Also note that this does not enable states + * disabled by pci_disable_link_state(). Return 0 or a negative errno. + * + * @pdev: PCI device + * @state: Mask of ASPM link states to enable + * + * Context: Caller holds pci_bus_sem read lock. + */ +int pci_enable_link_state_locked(struct pci_dev *pdev, int state) +{ + lockdep_assert_held_read(&pci_bus_sem); + + return __pci_enable_link_state(pdev, state, true); +} +EXPORT_SYMBOL(pci_enable_link_state_locked); + static int pcie_aspm_set_policy(const char *val, const struct kernel_param *kp) { diff --git a/include/linux/pci.h b/include/linux/pci.h index 60ca768bc867..dea043bc1e38 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1829,6 +1829,7 @@ extern bool pcie_ports_native; int pci_disable_link_state(struct pci_dev *pdev, int state); int pci_disable_link_state_locked(struct pci_dev *pdev, int state); int pci_enable_link_state(struct pci_dev *pdev, int state); +int pci_enable_link_state_locked(struct pci_dev *pdev, int state); void pcie_no_aspm(void); bool pcie_aspm_support_enabled(void); bool pcie_aspm_enabled(struct pci_dev *pdev); @@ -1839,6 +1840,8 @@ static inline int pci_disable_link_state_locked(struct pci_dev *pdev, int state) { return 0; } static inline int pci_enable_link_state(struct pci_dev *pdev, int state) { return 0; } +static inline int pci_enable_link_state_locked(struct pci_dev *pdev, int state) +{ return 0; } static inline void pcie_no_aspm(void) { } static inline bool pcie_aspm_support_enabled(void) { return false; } static inline bool pcie_aspm_enabled(struct pci_dev *pdev) { return false; }
Add a helper for enabling link states that can be used in contexts where a pci_bus_sem read lock is already held (e.g. from pci_walk_bus()). This helper will be used to fix a couple of potential deadlocks where the current helper is called with the lock already held, hence the CC stable tag. Fixes: f492edb40b54 ("PCI: vmd: Add quirk to configure PCIe ASPM and LTR") Cc: stable@vger.kernel.org # 6.3 Cc: Michael Bottini <michael.a.bottini@linux.intel.com> Cc: David E. Box <david.e.box@linux.intel.com> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> Signed-off-by: Johan Hovold <johan+linaro@kernel.org> --- drivers/pci/pcie/aspm.c | 53 +++++++++++++++++++++++++++++++---------- include/linux/pci.h | 3 +++ 2 files changed, 43 insertions(+), 13 deletions(-)