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charset="us-ascii" On Wed, Nov 04, 2026, sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > - [Medium] selftests/kvm: infinite loop when fopen() fails in get_run_delay() > -- > > commit fed2657e5d999eb78e5e508f23ea617f2787e14a > Author: zhangchujun > > selftests/kvm: check fopen() return in get_run_delay() > > This commit adds a NULL check on the FILE pointer returned by fopen() in > get_run_delay() so that it returns MIN_RUN_DELAY_NS instead of passing NULL to > fscanf() and fclose() when /proc//schedstat cannot be opened. > > > diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c > > index f5f7189f96a84..2827f7d7d905e 100644 > > --- a/tools/testing/selftests/kvm/lib/test_util.c > > +++ b/tools/testing/selftests/kvm/lib/test_util.c > > @@ -421,6 +421,8 @@ long get_run_delay(void) > > sprintf(path, "/proc/%ld/schedstat", (long)kvm_gettid()); > > fp = fopen(path, "r"); > > /* Return MIN_RUN_DELAY_NS upon failure just to be safe */ > > + if (!fp) > > + return MIN_RUN_DELAY_NS; > > [Severity: Medium] > If fopen() fails to open /proc//schedstat (for instance, when > CONFIG_SCHED_INFO is disabled in the host kernel), will returning the constant > MIN_RUN_DELAY_NS here cause the callers of get_run_delay() to hang in an > infinite loop? > > get_run_delay() reads the calling thread's cumulative scheduler run_delay > counter, and both callers in the tree wait for subsequent readings to advance > past an initial baseline. > > In tools/testing/selftests/kvm/steal_time.c:main(): > > run_delay = get_run_delay(); > kvm_pthread_create(&thread, NULL, do_steal_time, NULL); > kvm_pthread_getaffinity(thread, &cpuset); > TEST_ASSERT(CPU_COUNT(&cpuset) == 1 && CPU_ISSET(cpu, &cpuset), > "Worker failed to inherit parent's CPU affinity"); > > do > sched_yield(); > while (get_run_delay() - run_delay < MIN_RUN_DELAY_NS); > > When get_run_delay() returns MIN_RUN_DELAY_NS on every call, > get_run_delay() - run_delay evaluates to 0, which is always less than > MIN_RUN_DELAY_NS, causing this loop to spin forever. > > Similarly, in tools/testing/selftests/kvm/x86/xen_shinfo_test.c:main(): > > rundelay = get_run_delay() + MIN_STEAL_TIME; > do { > sched_yield(); > } while (get_run_delay() < rundelay); > > Here, rundelay becomes MIN_RUN_DELAY_NS + MIN_STEAL_TIME while get_run_delay() > continues returning MIN_RUN_DELAY_NS, which also spins forever. > > Should get_run_delay() instead fail or skip via TEST_ASSERT() or > TEST_REQUIRE() when fopen() fails, similar to other file-opening helpers in > tools/testing/selftests/kvm/lib/test_util.c such as get_sysfs_val() and > get_def_hugetlb_pagesz()? Ya, I agree with Sashiko. Not only could returning MIN_RUN_DELAY_NS lead to failure, it could result in false passes, which is arguably even worse. E.g. running the steal time test with CONFIG_SCHEDSTATS=n seems pointless. I don't think we want to simply do TEST_REQUIRE() if fopen() fails, because that would result in weird skips if fopen() initially succeeds but then randomly fails partway through the test. I think the best way to tackle this would be to provide separate APIs to open and read the file, and then have the open API do TEST_REQUIRE() and the read API do TEST_ASSERT(). E.g. FILE *sys_open_schedstat(void) { char path[64]; FILE *f; int fd; sprintf(path, "/proc/%ld/schedstat", (long)kvm_gettid()); fd = open_path_or_exit(path, O_RDONLY); f = fdopen(fd, "r"); TEST_ASSERT(f, __KVM_SYSCALL_ERROR("fdopen()", -1)); return f; } long get_run_delay(FILE *f) { long val[2]; int r; r = fscanf(f, "%ld %ld ", &val[0], &val[1]); TEST_ASSERT(r == 2, __KVM_SYSCALL_ERROR("fscanf()", r)); return val[1]; }