Re: [PATCH v4] KVM: selftests: Fix target thread to be migrated in rseq_test

On Tue, Jul 19, 2022 at 10:08:30AM +0800, Gavin Shan wrote:

In rseq_test, there are two threads, which are vCPU thread and migration worker separately. Unfortunately, the test has the wrong PID passed to sched_setaffinity() in the migration worker. It forces migration on the migration worker because zeroed PID represents the calling thread, which is the migration worker itself. It means the vCPU thread is never enforced to migration and it can migrate at any time, which eventually leads to failure as the following logs show.

host# uname -r 5.19.0-rc6-gavin+ host# # cat /proc/cpuinfo | grep processor | tail -n 1 processor : 223 host# pwd /home/gavin/sandbox/linux.main/tools/testing/selftests/kvm host# for i in `seq 1 100`; do \ echo "--------> $i"; ./rseq_test; done --------> 1 --------> 2 --------> 3 --------> 4 --------> 5 --------> 6 ==== Test Assertion Failure ==== rseq_test.c:265: rseq_cpu == cpu pid=3925 tid=3925 errno=4 - Interrupted system call 1 0x0000000000401963: main at rseq_test.c:265 (discriminator 2) 2 0x0000ffffb044affb: ?? ??:0 3 0x0000ffffb044b0c7: ?? ??:0 4 0x0000000000401a6f: _start at ??:? rseq CPU = 4, sched CPU = 27

Fix the issue by passing correct parameter, TID of the vCPU thread, to sched_setaffinity() in the migration worker.

Fixes: 61e52f1630f5 ("KVM: selftests: Add a test for KVM_RUN+rseq to detect task migration bugs") Suggested-by: Sean Christopherson seanjc@google.com Signed-off-by: Gavin Shan gshan@redhat.com Reviewed-by: Oliver Upton oliver.upton@linux.dev

---

v4: Pick the code change as Sean suggested.

tools/testing/selftests/kvm/rseq_test.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c index 4158da0da2bb..2237d1aac801 100644 --- a/tools/testing/selftests/kvm/rseq_test.c +++ b/tools/testing/selftests/kvm/rseq_test.c @@ -82,8 +82,9 @@ static int next_cpu(int cpu) return cpu; } -static void *migration_worker(void *ign) +static void *migration_worker(void *__rseq_tid) {

• pid_t rseq_tid = (pid_t)(unsigned long)__rseq_tid; cpu_set_t allowed_mask; int r, i, cpu;

@@ -106,7 +107,7 @@ static void *migration_worker(void *ign) * stable, i.e. while changing affinity is in-progress. */ smp_wmb();

• r = sched_setaffinity(0, sizeof(allowed_mask), &allowed_mask);
  

• r = sched_setaffinity(rseq_tid, sizeof(allowed_mask), &allowed_mask);
  

  TEST_ASSERT(!r, "sched_setaffinity failed, errno = %d (%s)", errno, strerror(errno)); smp_wmb();

@@ -231,7 +232,8 @@ int main(int argc, char *argv[]) vm = vm_create_default(VCPU_ID, 0, guest_code); ucall_init(vm, NULL);

• pthread_create(&migration_thread, NULL, migration_worker, 0);

• pthread_create(&migration_thread, NULL, migration_worker,

•        (void *)(unsigned long)gettid());
  

for (i = 0; !done; i++) { vcpu_run(vm, VCPU_ID); -- 2.23.0

Thanks for figuring this out Gavin and Sean!

Reviewed-by: Andrew Jones andrew.jones@linux.dev