linux-kernel - Re: [PATCH v4] KVM: selftests: Fix target thread to be migrated in rseq

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Message-ID: <2b9070bd-61b2-0057-003e-f6c46f6c34a8@redhat.com>
Date:   Tue, 19 Jul 2022 15:04:33 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Gavin Shan <gshan@...hat.com>, kvmarm@...ts.cs.columbia.edu
Cc:     linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        oliver.upton@...ux.dev, seanjc@...gle.com, shuah@...nel.org,
        maz@...nel.org, shan.gavin@...il.com
Subject: Re: [PATCH v4] KVM: selftests: Fix target thread to be migrated in
 rseq_test

On 7/19/22 04:08, 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@...gle.com>
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> Reviewed-by: Oliver Upton <oliver.upton@...ux.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);

Queued, thanks.

Paolo