Re: [PATCH] Fix a data race with goflag in rcutorture test

[Paolo Bonzini]

On Wed, Jan 22, 2025 at 2:59 PM Vitalii Mordan <mordan@ispras.ru> wrote:
>
> This patch addresses a potential data race involving the global variable
> goflag in the rcutorture test. The issue is resolved by adding the atomic
> qualifier to ensure proper synchronization.

Hello!

QEMU does not use _Atomic; in general, the C11 committee decision to
default to sequentially consistent atomics is a bad idea and we prefer
to annotate _accesses_ rather than _variables_ (yes, I'm aware that
volatile has the same issue!).

Can you redo the patch to access goflag with qatomic_read and qatomic_set?

Paolo

> Fixes: 8fda74a52b ("rcu: add rcutorture")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2750
> Signed-off-by: Vitalii Mordan <mordan@ispras.ru>
> ---
>  tests/unit/rcutorture.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tests/unit/rcutorture.c b/tests/unit/rcutorture.c
> index 7662081683..c4971632f8 100644
> --- a/tests/unit/rcutorture.c
> +++ b/tests/unit/rcutorture.c
> @@ -70,7 +70,7 @@ int nthreadsrunning;
>  #define GOFLAG_RUN  1
>  #define GOFLAG_STOP 2
>
> -static volatile int goflag = GOFLAG_INIT;
> +static _Atomic int goflag = GOFLAG_INIT;
>
>  #define RCU_READ_RUN 1000
>
> --
> 2.34.1
>