From: Brian Norris briannorris@chromium.org
[ Upstream commit 788019eb559fd0b365f501467ceafce540e377cc ]
Affinity-managed interrupts can be shut down and restarted during CPU hotunplug/plug. Thereby the interrupt may be left in an unexpected state. Specifically:
1. Interrupt is affine to CPU N 2. disable_irq() -> depth is 1 3. CPU N goes offline 4. irq_shutdown() -> depth is set to 1 (again) 5. CPU N goes online 6. irq_startup() -> depth is set to 0 (BUG! driver expects that the interrupt still disabled) 7. enable_irq() -> depth underflow / unbalanced enable_irq() warning
This is only a problem for managed interrupts and CPU hotplug, all other cases like request()/free()/request() truly needs to reset a possibly stale disable depth value.
Provide a startup function, which takes the disable depth into account, and invoked it for the managed interrupts in the CPU hotplug path.
This requires to change irq_shutdown() to do a depth increment instead of setting it to 1, which allows to retain the disable depth, but is harmless for the other code paths using irq_startup(), which will still reset the disable depth unconditionally to keep the original correct behaviour.
A kunit tests will be added separately to cover some of these aspects.
[ tglx: Massaged changelog ]
Suggested-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Brian Norris briannorris@chromium.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/all/20250514201353.3481400-2-briannorris@chromium.or... Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis of the commit and the current kernel code, here is my assessment: **YES** This commit should be backported to stable kernel trees. Here's my extensive analysis: ## Bug Analysis The commit fixes a critical bug in the interrupt subsystem's CPU hotplug handling that affects affinity-managed interrupts. The bug manifests as follows: 1. **Problem Scenario**: When a managed interrupt is disabled (depth=1), then its CPU goes offline causing `irq_shutdown()`, and later the CPU comes back online triggering `irq_startup()`, the disable depth accounting becomes corrupted. 2. **Current Broken Behavior** (from existing kernel code): - `irq_shutdown()` sets `desc->depth = 1` unconditionally (line seen in grep output) - `irq_startup()` sets `desc->depth = 0` unconditionally - This overwrites any previous disable state, violating the disable/enable balance 3. **User-Visible Impact**: The bug causes: - Unbalanced `enable_irq()` warnings - Interrupts being unexpectedly enabled during CPU hotplug - Potential system instability or incorrect device behavior ## Code Changes Analysis The fix makes surgical changes to preserve disable depth: ### 1. **irq_shutdown() Change** (kernel/irq/chip.c): ```c - desc->depth = 1; + /bin /bin.usr- is-merged /boot /dev /etc /home /init /lib /lib.usr-is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md Increment disable depth, so that a managed shutdown on + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md CPU hotunplug preserves the actual disabled state when the + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md CPU comes back online. See irq_startup_managed(). + linux-kernel/ + desc->depth++; ``` This preserves the original disable state instead of overwriting it. ### 2. **New irq_startup_managed() Function**: ```c +void irq_startup_managed(struct irq_desc *desc) +{ + /bin /bin.usr-is-merged /boot /dev /etc /home /init /lib /lib.usr-is-merged /lib64 /lost+found /media /mnt /opt /proc /root /run /sbin /sbin.usr-is-merged /snap /srv /sys /tmp /usr /var + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md Only start it up when the disable depth is 1, so that a disable, + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md hotunplug, hotplug sequence does not end up enabling it during + amd_display_timing_generator_analysis.md amd_doorbell_analysis_framework.md amd_gpu_documentation_backport_analysis.md amd_si_chip_analysis.md amdgpu_csb_analysis.md amdgpu_mqd_prop_backport_analysis.md analogix_dp_backport_analysis.md cgroup_rstat_analysis.sh cgroup_rstat_analysis_guide.md cpuset_comment_fix_backport_analysis.md csiphy_x1e80100_backport_analysis.md dcn315_smu_indirect_register_access_analysis.md drm_dp_helper_dpcd_refactoring_backport_analysis.md drm_format_helper_generic_8bit_conversion_backport_analysis.md es8375_codec_driver_backport_analysis.md expected_findings_summary.md hdmi_read_request_analysis.md kernel_analysis_commands.sh kselftest_harness_teardown_metadata_backport_analysis.md linux-kernel mediatek_vcodec_h264_backport_analysis.md pidfd_open_kselftest_harness_compatibility_analysis.md qualcomm_camss_bus_type_backport_analysis.md selftests_harness_libatomic_backport_analysis.md sphinx_version_compatibility_backport_analysis.md spi_sh_msiof_grpmask_backport_analysis.md spi_sh_msiof_sitmdr2_sirmdr2_bitfield_conversion_backport_analysis.md sta2x11_removal_analysis.md test_unused_param.c test_unused_param.o ti_bridge_encoder_crtc_refactoring_backport_analysis.md xe_driver_flr_vf_restriction_analysis.md xe_firmware_per_gt_backport_analysis.md xe_sriov_logging_backport_analysis.md hotplug unconditionally. + linux- kernel/ + desc->depth--; + if (!desc->depth) + irq_startup(desc, IRQ_RESEND, IRQ_START_COND); +} ``` This provides proper depth-aware startup specifically for managed interrupts. ### 3. **IRQ_STARTUP_ABORT Case Update**: ```c case IRQ_STARTUP_ABORT: + desc->depth = 1; irqd_set_managed_shutdown(d); return 0; ``` Ensures consistent depth handling in abort cases. ### 4. **CPU Hotplug Integration** (kernel/irq/cpuhotplug.c): ```c - irq_startup(desc, IRQ_RESEND, IRQ_START_COND); + irq_startup_managed(desc); ``` Uses the new depth- aware function for managed interrupt restoration. ## Backport Suitability Assessment **Meets All Stable Criteria:** 1. **Fixes Important Bug**: ✅ Corrects interrupt enable/disable balance corruption 2. **Small & Contained**: ✅ Minimal changes confined to IRQ subsystem 3. **Low Regression Risk**: ✅ Only affects managed interrupts during CPU hotplug 4. **No New Features**: ✅ Pure bug fix, no architectural changes 5. **Critical Subsystem**: ✅ IRQ handling is fundamental to system stability **Similar Pattern Match**: This closely resembles Similar Commit #3 and #5 (both marked YES) which also fix managed interrupt CPU hotplug issues with surgical changes to preserve state across hotplug events. **Real-World Impact**: The bug can cause: - Server/datacenter systems using CPU hotplug for power management to experience interrupt handling issues - Multi-queue device drivers to malfunction after CPU hotplug cycles - Unbalanced IRQ state leading to system instability The fix is well-contained, addresses a clear functional bug with user- visible symptoms, and follows established patterns for stable backports in the IRQ subsystem.
kernel/irq/chip.c | 22 +++++++++++++++++++++- kernel/irq/cpuhotplug.c | 2 +- kernel/irq/internals.h | 1 + 3 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c index c901436ebd9f4..7abe050b7c656 100644 --- a/kernel/irq/chip.c +++ b/kernel/irq/chip.c @@ -223,6 +223,19 @@ __irq_startup_managed(struct irq_desc *desc, const struct cpumask *aff, return IRQ_STARTUP_ABORT; return IRQ_STARTUP_MANAGED; } + +void irq_startup_managed(struct irq_desc *desc) +{ + /* + * Only start it up when the disable depth is 1, so that a disable, + * hotunplug, hotplug sequence does not end up enabling it during + * hotplug unconditionally. + */ + desc->depth--; + if (!desc->depth) + irq_startup(desc, IRQ_RESEND, IRQ_START_COND); +} + #else static __always_inline int __irq_startup_managed(struct irq_desc *desc, const struct cpumask *aff, @@ -275,6 +288,7 @@ int irq_startup(struct irq_desc *desc, bool resend, bool force) ret = __irq_startup(desc); break; case IRQ_STARTUP_ABORT: + desc->depth = 1; irqd_set_managed_shutdown(d); return 0; } @@ -307,7 +321,13 @@ void irq_shutdown(struct irq_desc *desc) { if (irqd_is_started(&desc->irq_data)) { clear_irq_resend(desc); - desc->depth = 1; + /* + * Increment disable depth, so that a managed shutdown on + * CPU hotunplug preserves the actual disabled state when the + * CPU comes back online. See irq_startup_managed(). + */ + desc->depth++; + if (desc->irq_data.chip->irq_shutdown) { desc->irq_data.chip->irq_shutdown(&desc->irq_data); irq_state_set_disabled(desc); diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c index 15a7654eff684..3ed5b15927355 100644 --- a/kernel/irq/cpuhotplug.c +++ b/kernel/irq/cpuhotplug.c @@ -219,7 +219,7 @@ static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned int cpu) return;
if (irqd_is_managed_and_shutdown(data)) - irq_startup(desc, IRQ_RESEND, IRQ_START_COND); + irq_startup_managed(desc);
/* * If the interrupt can only be directed to a single target diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h index a979523640d0a..9661527e81571 100644 --- a/kernel/irq/internals.h +++ b/kernel/irq/internals.h @@ -87,6 +87,7 @@ extern void __enable_irq(struct irq_desc *desc); extern int irq_activate(struct irq_desc *desc); extern int irq_activate_and_startup(struct irq_desc *desc, bool resend); extern int irq_startup(struct irq_desc *desc, bool resend, bool force); +extern void irq_startup_managed(struct irq_desc *desc);
extern void irq_shutdown(struct irq_desc *desc); extern void irq_shutdown_and_deactivate(struct irq_desc *desc);