Re: [Qemu-devel] [PATCH v3 1/2] linux-aio: properly bubble up errors from initialization

[Fam Zheng <famz@redhat.com>]

On Thu, 06/21 15:21, Nishanth Aravamudan wrote:
> laio_init() can fail for a couple of reasons, which will lead to a NULL
> pointer dereference in laio_attach_aio_context().
> 
> To solve this, add a aio_setup_linux_aio() function which is called
> early in raw_open_common. If this fails, propagate the error up. The
> signature of aio_get_linux_aio() was not modified, because it seems
> preferable to return the actual errno from the possible failing
> initialization calls.
> 
> Add an assert that aio_get_linux_aio() cannot return NULL.
> 
> Signed-off-by: Nishanth Aravamudan <naravamudan@digitalocean.com>
> ---
> Changes from v2 -> v3 (thanks to Eric Blake and Kevin Wolf for review):
> 
> Use a boolean false rather than 0 in assignment to use_linux_aio.
> Drop ending '.' from error_report() calls.
> Fix typo in commit message (propogates -> propagates).
> Move aio_setup_linux_aio call to raw_open_common.
> 
> Changes from v1 -> v2 (thanks to Kevin Wolf for review):
> 
> Rather than affect virtio-scsi/blk at all, make all the changes internal
> to file-posix.c. Thanks to Kevin Wolf for the suggested change.
> 
>  block/file-posix.c      | 17 ++++++++++++-----
>  block/linux-aio.c       | 15 ++++++++++-----
>  include/block/aio.h     |  3 +++
>  include/block/raw-aio.h |  2 +-
>  stubs/linux-aio.c       |  2 +-
>  util/async.c            | 16 +++++++++++++---
>  6 files changed, 40 insertions(+), 15 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 07bb061fe4..6a1714d4a8 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -545,11 +545,18 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
>  
>  #ifdef CONFIG_LINUX_AIO
>       /* Currently Linux does AIO only for files opened with O_DIRECT */
> -    if (s->use_linux_aio && !(s->open_flags & O_DIRECT)) {
> -        error_setg(errp, "aio=native was specified, but it requires "
> -                         "cache.direct=on, which was not specified.");
> -        ret = -EINVAL;
> -        goto fail;
> +    if (s->use_linux_aio) {
> +        if (!(s->open_flags & O_DIRECT)) {
> +            error_setg(errp, "aio=native was specified, but it requires "
> +                             "cache.direct=on, which was not specified.");
> +            ret = -EINVAL;
> +            goto fail;
> +        }
> +        ret = aio_setup_linux_aio(bdrv_get_aio_context(bs));
> +        if (ret != 0) {
> +            error_setg(errp, "Unable to setup native AIO context.");
> +            goto fail;
> +        }
>      }
>  #else
>      if (s->use_linux_aio) {
> diff --git a/block/linux-aio.c b/block/linux-aio.c
> index 88b8d55ec7..4d799f85fe 100644
> --- a/block/linux-aio.c
> +++ b/block/linux-aio.c
> @@ -470,28 +470,33 @@ void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
>                             qemu_laio_poll_cb);
>  }
>  
> -LinuxAioState *laio_init(void)
> +int laio_init(LinuxAioState **linux_aio)
>  {
> +    int rc;
>      LinuxAioState *s;
>  
>      s = g_malloc0(sizeof(*s));
> -    if (event_notifier_init(&s->e, false) < 0) {
> +    rc = event_notifier_init(&s->e, false);
> +    if (rc < 0) {

It would be nice if the error message could distinguish this error...

>          goto out_free_state;
>      }
>  
> -    if (io_setup(MAX_EVENTS, &s->ctx) != 0) {
> +    rc = io_setup(MAX_EVENTS, &s->ctx);
> +    if (rc != 0) {

... from this one. And it also makes sense to propagate the errno back with
error_setg_errno.

To do this, add an "Error **errp" parameter to the function and you can keep the
return type (LinuxAioState *).

>          goto out_close_efd;
>      }
>  
>      ioq_init(&s->io_q);
>  
> -    return s;
> +    *linux_aio = s;
> +    return 0;
>  
>  out_close_efd:
>      event_notifier_cleanup(&s->e);
>  out_free_state:
>      g_free(s);
> -    return NULL;
> +    *linux_aio = NULL;
> +    return rc;
>  }
>  
>  void laio_cleanup(LinuxAioState *s)
> diff --git a/include/block/aio.h b/include/block/aio.h
> index ae6f354e6c..8900516ac5 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -381,6 +381,9 @@ GSource *aio_get_g_source(AioContext *ctx);
>  /* Return the ThreadPool bound to this AioContext */
>  struct ThreadPool *aio_get_thread_pool(AioContext *ctx);
>  
> +/* Setup the LinuxAioState bound to this AioContext */
> +int aio_setup_linux_aio(AioContext *ctx);

And this will then need "Error **errp" as well.

> +
>  /* Return the LinuxAioState bound to this AioContext */
>  struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
>  
> diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
> index 0e717fd475..81b90e5fc6 100644
> --- a/include/block/raw-aio.h
> +++ b/include/block/raw-aio.h
> @@ -43,7 +43,7 @@
>  /* linux-aio.c - Linux native implementation */
>  #ifdef CONFIG_LINUX_AIO
>  typedef struct LinuxAioState LinuxAioState;
> -LinuxAioState *laio_init(void);
> +int laio_init(LinuxAioState **linux_aio);
>  void laio_cleanup(LinuxAioState *s);
>  int coroutine_fn laio_co_submit(BlockDriverState *bs, LinuxAioState *s, int fd,
>                                  uint64_t offset, QEMUIOVector *qiov, int type);
> diff --git a/stubs/linux-aio.c b/stubs/linux-aio.c
> index ed47bd443c..88ab927e35 100644
> --- a/stubs/linux-aio.c
> +++ b/stubs/linux-aio.c
> @@ -21,7 +21,7 @@ void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context)
>      abort();
>  }
>  
> -LinuxAioState *laio_init(void)
> +int laio_init(LinuxAioState **linux_aio)
>  {
>      abort();
>  }
> diff --git a/util/async.c b/util/async.c
> index 03f62787f2..ae88c931d0 100644
> --- a/util/async.c
> +++ b/util/async.c
> @@ -323,12 +323,22 @@ ThreadPool *aio_get_thread_pool(AioContext *ctx)
>  }
>  
>  #ifdef CONFIG_LINUX_AIO
> -LinuxAioState *aio_get_linux_aio(AioContext *ctx)
> +int aio_setup_linux_aio(AioContext *ctx)
>  {
> +    int rc;
> +    rc = 0;
>      if (!ctx->linux_aio) {
> -        ctx->linux_aio = laio_init();
> -        laio_attach_aio_context(ctx->linux_aio, ctx);
> +        rc = laio_init(&ctx->linux_aio);
> +        if (rc == 0) {
> +            laio_attach_aio_context(ctx->linux_aio, ctx);
> +        }
>      }
> +    return rc;
> +}
> +
> +LinuxAioState *aio_get_linux_aio(AioContext *ctx)
> +{
> +    assert(ctx->linux_aio);
>      return ctx->linux_aio;
>  }
>  #endif
> -- 
> 2.17.1
> 

Fam