lwn.git/drivers/clocksource, branch master

clocksource: Rewrite watchdog code completely

2026-03-20T12:36:32+00:00

The clocksource watchdog code has over time reached the state of an impenetrable maze of duct tape and staples. The original design, which was made in the context of systems far smaller than today, is based on the assumption that the to be monitored clocksource (TSC) can be trivially compared against a known to be stable clocksource (HPET/ACPI-PM timer). Over the years it turned out that this approach has major flaws: - Long delays between watchdog invocations can result in wrap arounds of the reference clocksource - Scalability of the reference clocksource readout can degrade on large multi-socket systems due to interconnect congestion This was addressed with various heuristics which degraded the accuracy of the watchdog to the point that it fails to detect actual TSC problems on older hardware which exposes slow inter CPU drifts due to firmware manipulating the TSC to hide SMI time. To address this and bring back sanity to the watchdog, rewrite the code completely with a different approach: 1) Restrict the validation against a reference clocksource to the boot CPU, which is usually the CPU/Socket closest to the legacy block which contains the reference source (HPET/ACPI-PM timer). Validate that the reference readout is within a bound latency so that the actual comparison against the TSC stays within 500ppm as long as the clocks are stable. 2) Compare the TSCs of the other CPUs in a round robin fashion against the boot CPU in the same way the TSC synchronization on CPU hotplug works. This still can suffer from delayed reaction of the remote CPU to the SMP function call and the latency of the control variable cache line. But this latency is not affecting correctness. It only affects the accuracy. With low contention the readout latency is in the low nanoseconds range, which detects even slight skews between CPUs. Under high contention this becomes obviously less accurate, but still detects slow skews reliably as it solely relies on subsequent readouts being monotonically increasing. It just can take slightly longer to detect the issue. 3) Rewrite the watchdog test so it tests the various mechanisms one by one and validating the result against the expectation. Signed-off-by: Thomas Gleixner Tested-by: Borislav Petkov (AMD) Tested-by: Daniel J Blueman Reviewed-by: Jiri Wiesner Reviewed-by: Daniel J Blueman Link: https://patch.msgid.link/20260123231521.926490888@kernel.org Link: https://patch.msgid.link/87h5qeomm5.ffs@tglx

MIPS: Don't select CLOCKSOURCE_WATCHDOG

2026-03-12T11:23:26+00:00

MIPS selects CLOCKSOURCE_WATCHDOG, but none of the clocksources actually sets the MUST_VERIFY flag. So compiling the watchdog in is a pointless exercise. Remove the selects. Signed-off-by: Thomas Gleixner Signed-off-by: Thomas Gleixner Link: https://patch.msgid.link/20260123231521.723433371@kernel.org

Convert remaining multi-line kmalloc_obj/flex GFP_KERNEL uses

2026-02-22T16:26:33+00:00

Conversion performed via this Coccinelle script: // SPDX-License-Identifier: GPL-2.0-only // Options: --include-headers-for-types --all-includes --include-headers --keep-comments virtual patch @gfp depends on patch && !(file in "tools") && !(file in "samples")@ identifier ALLOC = {kmalloc_obj,kmalloc_objs,kmalloc_flex, kzalloc_obj,kzalloc_objs,kzalloc_flex, kvmalloc_obj,kvmalloc_objs,kvmalloc_flex, kvzalloc_obj,kvzalloc_objs,kvzalloc_flex}; @@ ALLOC(... - , GFP_KERNEL ) $ make coccicheck MODE=patch COCCI=gfp.cocci Build and boot tested x86_64 with Fedora 42's GCC and Clang: Linux version 6.19.0+ (user@host) (gcc (GCC) 15.2.1 20260123 (Red Hat 15.2.1-7), GNU ld version 2.44-12.fc42) #1 SMP PREEMPT_DYNAMIC 1970-01-01 Linux version 6.19.0+ (user@host) (clang version 20.1.8 (Fedora 20.1.8-4.fc42), LLD 20.1.8) #1 SMP PREEMPT_DYNAMIC 1970-01-01 Signed-off-by: Kees Cook Signed-off-by: Linus Torvalds

Convert more 'alloc_obj' cases to default GFP_KERNEL arguments

2026-02-22T04:03:00+00:00

This converts some of the visually simpler cases that have been split over multiple lines. I only did the ones that are easy to verify the resulting diff by having just that final GFP_KERNEL argument on the next line. Somebody should probably do a proper coccinelle script for this, but for me the trivial script actually resulted in an assertion failure in the middle of the script. I probably had made it a bit _too_ trivial. So after fighting that far a while I decided to just do some of the syntactically simpler cases with variations of the previous 'sed' scripts. The more syntactically complex multi-line cases would mostly really want whitespace cleanup anyway. Signed-off-by: Linus Torvalds

Convert 'alloc_flex' family to use the new default GFP_KERNEL argument

2026-02-22T01:09:51+00:00

This is the exact same thing as the 'alloc_obj()' version, only much smaller because there are a lot fewer users of the *alloc_flex() interface. As with alloc_obj() version, this was done entirely with mindless brute force, using the same script, except using 'flex' in the pattern rather than 'objs*'. Signed-off-by: Linus Torvalds

Convert 'alloc_obj' family to use the new default GFP_KERNEL argument

2026-02-22T01:09:51+00:00

This was done entirely with mindless brute force, using git grep -l '\

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook

Merge tag 'x86_paravirt_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-02-11T03:01:45+00:00

Pull x86 paravirt updates from Borislav Petkov: - A nice cleanup to the paravirt code containing a unification of the paravirt clock interface, taming the include hell by splitting the pv_ops structure and removing of a bunch of obsolete code (Juergen Gross) * tag 'x86_paravirt_for_v7.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (23 commits) x86/paravirt: Use XOR r32,r32 to clear register in pv_vcpu_is_preempted() x86/paravirt: Remove trailing semicolons from alternative asm templates x86/pvlocks: Move paravirt spinlock functions into own header x86/paravirt: Specify pv_ops array in paravirt macros x86/paravirt: Allow pv-calls outside paravirt.h objtool: Allow multiple pv_ops arrays x86/xen: Drop xen_mmu_ops x86/xen: Drop xen_cpu_ops x86/xen: Drop xen_irq_ops x86/paravirt: Move pv_native_*() prototypes to paravirt.c x86/paravirt: Introduce new paravirt-base.h header x86/paravirt: Move paravirt_sched_clock() related code into tsc.c x86/paravirt: Use common code for paravirt_steal_clock() riscv/paravirt: Use common code for paravirt_steal_clock() loongarch/paravirt: Use common code for paravirt_steal_clock() arm64/paravirt: Use common code for paravirt_steal_clock() arm/paravirt: Use common code for paravirt_steal_clock() sched: Move clock related paravirt code to kernel/sched paravirt: Remove asm/paravirt_api_clock.h x86/paravirt: Move thunk macros to paravirt_types.h ...

Merge tag 'timers-clocksource-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-02-11T00:37:54+00:00

Pull clocksource updates from Thomas Gleixner: "A rather small set of boring cleanups, fixes and improvements" * tag 'timers-clocksource-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: clocksource/drivers/mips-gic-timer: Move GIC timer to request_percpu_irq() clocksource/drivers/timer-sp804: Fix an Oops when read_current_timer is called on ARM32 platforms where the SP804 is not registered as the sched_clock. clocksource/drivers/armada-370-xp: Fix dead link to timer binding clocksource/drivers/timer-integrator-ap: Add missing Kconfig dependency on OF clocksource/drivers/sh_tmu: Always leave device running after probe

Merge tag 'irq-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2026-02-10T21:39:37+00:00

Pull irq core updates from Thomas Gleixner: "Updates for the interrupt core subsystem: - Remove the interrupt timing infrastructure This was added seven years ago to be used for power management purposes, but that integration never happened. - Clean up the remaining setup_percpu_irq() users The memory allocator is available when interrupts can be requested so there is not need for static irq_action. Move the remaining users to request_percpu_irq() and delete the historical cruft. - Warn when interrupt flag inconsistencies are detected in request*_irq(). Inconsistent flags can lead to hard to diagnose malfunction. The fallout of this new warning has been addressed in next and the fixes are coming in via the maintainer trees and the tip irq/cleanup pull requests. - Invoke affinity notifier when CPU hotplug breaks affinity Otherwise the code using the notifier misses the affinity change and operates on stale information. - The usual cleanups and improvements" * tag 'irq-core-2026-02-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: genirq/proc: Replace snprintf with strscpy in register_handler_proc genirq/cpuhotplug: Notify about affinity changes breaking the affinity mask genirq: Move clear of kstat_irqs to free_desc() genirq: Warn about using IRQF_ONESHOT without a threaded handler irqdomain: Fix up const problem in irq_domain_set_name() genirq: Remove setup_percpu_irq() clocksource/drivers/mips-gic-timer: Move GIC timer to request_percpu_irq() MIPS: Move IP27 timer to request_percpu_irq() MIPS: Move IP30 timer to request_percpu_irq() genirq: Remove __request_percpu_irq() helper genirq: Remove IRQ timing tracking infrastructure