Re: [RESEND PATCH] hw/dma: fix crash caused by race condition

[Laurent Vivier]

Le 06/05/2022 à 18:31, Tong Zhang a écrit :
> assert(dbs->acb) is meant to check the return value of io_func per
> documented in commit 6bee44ea34 ("dma: the passed io_func does not
> return NULL"). However, there is a chance that after calling
> aio_context_release(dbs->ctx); the dma_blk_cb function is called before
> the assertion and dbs->acb is set to NULL again at line 121. Thus when
> we run assert at line 181 it will fail.
>
>    softmmu/dma-helpers.c:181: dma_blk_cb: Assertion `dbs->acb' failed.
>
> Reported-by: Francisco Londono <f.londono@samsung.com>
> Signed-off-by: Tong Zhang <t.zhang2@samsung.com>
> ---
>   softmmu/dma-helpers.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/softmmu/dma-helpers.c b/softmmu/dma-helpers.c
> index 7820fec54c..cb81017928 100644
> --- a/softmmu/dma-helpers.c
> +++ b/softmmu/dma-helpers.c
> @@ -177,8 +177,8 @@ static void dma_blk_cb(void *opaque, int ret)
>       aio_context_acquire(dbs->ctx);
>       dbs->acb = dbs->io_func(dbs->offset, &dbs->iov,
>                               dma_blk_cb, dbs, dbs->io_func_opaque);
> -    aio_context_release(dbs->ctx);
>       assert(dbs->acb);
> +    aio_context_release(dbs->ctx);
>   }
>   
>   static void dma_aio_cancel(BlockAIOCB *acb)

Fixes: 1919631e6b55 ("block: explicitly acquire aiocontext in bottom halves that 
need it")
Reviewed-by: Laurent Vivier <laurent@vivier.eu>