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X-Proofpoint-GUID: lSnCML5FKNtE_vy93FyUIwBcYGrXzWpd X-Proofpoint-ORIG-GUID: lSnCML5FKNtE_vy93FyUIwBcYGrXzWpd sashiko-bot@kernel.org writes: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [Low] Module linkage failure due to unexported symbol `arch_timer_evtstrm_available`. > -- > > commit 6f96330ea583f1ff6aede67a83cdc552196dad11 > Author: Ankur Arora > > arm64: barrier: Support smp_cond_load_relaxed_timeout() > > This commit introduces an optimized cpu_poll_relax() for ARM64 that uses > __cmpwait_relaxed() to wait for a value change. It gates this logic on > arch_timer_evtstrm_available() being true to avoid blocking forever without > periodic wakeups from the event stream. > >> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h >> --- a/arch/arm64/include/asm/barrier.h >> +++ b/arch/arm64/include/asm/barrier.h > > [ ... ] > >> +/* Re-declared here to avoid include dependency. */ >> +extern bool arch_timer_evtstrm_available(void); >> + >> +/* >> + * In the common case, cpu_poll_relax() sits waiting in __cmpwait_relaxed() >> + * for @ptr value to change. >> + * >> + * State this by defining CPU_POLL_RELAX_WAITS which enables a time-check >> + * optimization in smp_cond_load_{relaxed,acquire}_timeout(). >> + */ >> +#define CPU_POLL_RELAX_WAITS >> + >> +#define cpu_poll_relax(ptr, val, timeout_ns) do { \ >> + if (arch_timer_evtstrm_available()) \ >> + __cmpwait_relaxed(ptr, val); \ >> + else \ >> + cpu_relax(); \ >> +} while (0) > > [Severity: Low] > Will this cause a module linkage failure if a loadable kernel module > uses smp_cond_load_relaxed_timeout() or similar APIs? > > Since cpu_poll_relax() is a macro, it expands directly in the caller's > code. However, looking at drivers/clocksource/arm_arch_timer.c, it appears > that arch_timer_evtstrm_available() is not exported to loadable modules: > > drivers/clocksource/arm_arch_timer.c:arch_timer_evtstrm_available() { > /* > * We might get called from a preemptible context. > ... > } > > Without an EXPORT_SYMBOL declaration, any loadable module utilizing this > polling macro will fail to link with an unknown symbol error. Should > arch_timer_evtstrm_available be exported to support loadable modules? As mentioned in https://lore.kernel.org/all/87qzkk2hxz.fsf@oracle.com/: This interface mostly exists (or wants to) to unify spin-wait with timeout where the waiting can be done via a spinning cpu_relax() or arm64 style waiting on a cacheline (WFE/WFET). Currently, almost all of the users of smp_cond_load_{acquire,relaxed} are in kernel/ $ git grep -E 'smp_cond_load_acquire|smp_cond_load_relaxed' kernel/ | wc 27 145 2191 The only non kernel/ users are in: $ git grep -E 'smp_cond_load_acquire|smp_cond_load_relaxed' arch/ drivers/ mm/ fs/ arch/arm64/include/asm/mte.h: smp_cond_load_acquire(&page->flags.f, VAL & (1UL << PG_mte_tagged)); arch/arm64/include/asm/mte.h: smp_cond_load_acquire(&folio->flags.f, VAL & (1UL << PG_mte_tagged)); arch/arm64/mm/mmu.c: smp_cond_load_acquire(&idmap_kpti_bbml2_flag, VAL == num_online_cpus()); drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c: smp_cond_load_relaxed(cmd, !VAL || (ret = queue_poll(&qp))); So I don't expect this to be needed in kernel modules any time soon. And if it is, we can export the symbol then. -- ankur