Re: [PATCH 11/13] block/fuse: take AioContext lock around blk_exp_ref/unref()

[Paolo Bonzini]

On 4/3/23 20:30, Stefan Hajnoczi wrote:
> These functions must be called with the AioContext acquired:
>
>    /* Callers must hold exp->ctx lock */
>    void blk_exp_ref(BlockExport *exp)
>    ...
>    /* Callers must hold exp->ctx lock */
>    void blk_exp_unref(BlockExport *exp)
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   block/export/fuse.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/block/export/fuse.c b/block/export/fuse.c
> index 06fa41079e..18394f9e07 100644
> --- a/block/export/fuse.c
> +++ b/block/export/fuse.c
> @@ -244,7 +244,9 @@ static void read_from_fuse_export(void *opaque)
>       FuseExport *exp = opaque;
>       int ret;
>   
> +    aio_context_acquire(exp->common.ctx);
>       blk_exp_ref(&exp->common);
> +    aio_context_release(exp->common.ctx);
>   
>       do {
>           ret = fuse_session_receive_buf(exp->fuse_session, &exp->fuse_buf);
> @@ -256,7 +258,9 @@ static void read_from_fuse_export(void *opaque)
>       fuse_session_process_buf(exp->fuse_session, &exp->fuse_buf);
>   
>   out:
> +    aio_context_acquire(exp->common.ctx);
>       blk_exp_unref(&exp->common);
> +    aio_context_release(exp->common.ctx);
>   }

Since the actual thread-unsafe work is done in a bottom half, perhaps 
instead you can use qatomic_inc and qatomic_fetch_dec in 
blk_exp_{ref,unref}?

Paolo