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cc=ntf awl=host:13521 X-Proofpoint-GUID: Gmq8F13qHLje26p02RjPxiZrzRI2KT7q X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA0MDE4OCBTYWx0ZWRfX7QWn+nWTFZe8 lxr1wgwAffzSvcWTeH0XMQonVPLshlK1cWk4SQ2eg1y3A7iPS/2G/rVkpGmDEjg6epNJxIJnAb3 PLLbr1HcVKHN0kJIEkzuQhqUjJkgkLceoCriJYJt8RPxwKjQdMAB The implementation of this selftest program borrows from tools/testing/selftests/kvm/steal_time.c. The same concerns also apply to tools/testing/selftests/kvm/steal_time.c. Based on my understanding, KVM selftests do not require strict error-handling code. Thank you very much! Dongli Zhang On Fri, Sep 4, 2026 11:11:03AM -0700, sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: > - [Medium] The delay accumulation loop can hang indefinitely because the background thread uses a fixed wall-clock timeout instead of synchronizing with the main thread. > - [Medium] Unchecked return values from pthread APIs lead to undefined behavior and potential test hangs. > -- > > commit 4093ded4f0187a7d185578eeea38cf167b09f1d2 > Author: Dongli Zhang > > KVM: selftests: Test steal time across vCPU pid changes on x86 > > This commit adds a selftest to verify that KVM correctly resets steal-time > accounting when a vCPU is run from a new host thread. It creates a background > thread to accumulate run delay and checks if the steal time remains monotonic > across PID changes. > >> --- /dev/null >> +++ b/tools/testing/selftests/kvm/steal_time_change_pid.c >> @@ -0,0 +1,162 @@ > [ ... ] >> +static void *do_steal_time(void *arg) >> +{ >> + struct timespec ts, stop; >> + >> + clock_gettime(CLOCK_MONOTONIC, &ts); >> + stop = timespec_add_ns(ts, MIN_RUN_DELAY_NS); >> + >> + while (timespec_to_ns(timespec_sub(ts, stop)) < 0) >> + clock_gettime(CLOCK_MONOTONIC, &ts); > > [Severity: Medium] > Does this background thread rely on a fixed wall-clock timeout instead of > synchronizing with the main thread's delay accumulation? > > If scheduler interleaving allows the main thread to run during this window, > its accumulated run delay will be strictly less than MIN_RUN_DELAY_NS when > this thread exits. Once this thread exits, CPU 0 becomes uncontended and > the main thread's delay accumulation loop will hang indefinitely. > >> + >> + return NULL; >> +} > [ ... ] >> +int main(void) >> +{ >> + struct kvm_vcpu *vcpu; >> + struct kvm_vm *vm; >> + pthread_attr_t attr; >> + pthread_t thread; >> + cpu_set_t cpuset; >> + long run_delay; >> + long run_delay_delta; >> + >> + ksft_print_header(); >> + ksft_set_plan(1); >> + >> + CPU_ZERO(&cpuset); >> + CPU_SET(0, &cpuset); >> + pthread_attr_init(&attr); >> + pthread_attr_setaffinity_np(&attr, sizeof(cpuset), &cpuset); >> + pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset); > > [Severity: Medium] > If this pthread_setaffinity_np call fails (for example, if CPU 0 is not in > the allowed task mask), could the threads run on different CPUs? This would > prevent the main thread from ever accumulating runqueue wait time, causing it > to hang forever in the sched_yield loop. > > [ ... ] >> + run_delay = get_run_delay(); >> + pthread_create(&thread, &attr, do_steal_time, NULL); > > [Severity: Medium] > If pthread_create fails due to resource limits, will the thread variable > remain uninitialized? > >> + >> + while (get_run_delay() - run_delay < MIN_RUN_DELAY_NS) >> + sched_yield(); > > [Severity: Medium] > As mentioned above, if do_steal_time exits before MIN_RUN_DELAY_NS is > accumulated by the main thread, does this spinloop hang permanently because > the background thread is no longer consuming CPU time? > >> + >> + pthread_join(thread, NULL); > > [Severity: Medium] > If the thread variable is uninitialized due to a prior pthread_create > failure, does passing it unconditionally to pthread_join invoke undefined > behavior? >