Re: [PATCH 03/13] block: Revert .bdrv_drained_begin/end to non-coroutine_fn

[Stefan Hajnoczi]

On Tue, Nov 08, 2022 at 01:37:28PM +0100, Kevin Wolf wrote:
> Polling during bdrv_drained_end() can be problematic (and in the future,
> we may get cases for bdrv_drained_begin() where polling is forbidden,
> and we don't care about already in-flight requests, but just want to
> prevent new requests from arriving).
> 
> The .bdrv_drained_begin/end callbacks running in a coroutine is the only
> reason why we have to do this polling, so make them non-coroutine
> callbacks again. None of the callers actually yield any more.
> 
> This means that bdrv_drained_end() effectively doesn't poll any more,
> even if AIO_WAIT_WHILE() loops are still there (their condition is false
> from the beginning). This is generally not a problem, but in
> test-bdrv-drain, some additional explicit aio_poll() calls need to be
> added because the test case wants to verify the final state after BHs
> have executed.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  include/block/block_int-common.h | 10 ++++---
>  block.c                          |  4 +--
>  block/io.c                       | 49 +++++---------------------------
>  block/qed.c                      |  4 +--
>  block/throttle.c                 |  6 ++--
>  tests/unit/test-bdrv-drain.c     | 18 ++++++------
>  6 files changed, 30 insertions(+), 61 deletions(-)

Wow, surprisingly little has to change to make these non-coroutine_fn.

> 
> diff --git a/include/block/block_int-common.h 
> b/include/block/block_int-common.h
> index 5a2cc077a0..0956acbb60 100644
> --- a/include/block/block_int-common.h
> +++ b/include/block/block_int-common.h
> @@ -735,17 +735,19 @@ struct BlockDriver {
>      void (*bdrv_io_unplug)(BlockDriverState *bs);
>  
>      /**
> -     * bdrv_co_drain_begin is called if implemented in the beginning of a
> +     * bdrv_drain_begin is called if implemented in the beginning of a
>       * drain operation to drain and stop any internal sources of requests in
>       * the driver.
> -     * bdrv_co_drain_end is called if implemented at the end of the drain.
> +     * bdrv_drain_end is called if implemented at the end of the drain.
>       *
>       * They should be used by the driver to e.g. manage scheduled I/O
>       * requests, or toggle an internal state. After the end of the drain new
>       * requests will continue normally.
> +     *
> +     * Implementations of both functions must not call aio_poll().
>       */
> -    void coroutine_fn (*bdrv_co_drain_begin)(BlockDriverState *bs);
> -    void coroutine_fn (*bdrv_co_drain_end)(BlockDriverState *bs);
> +    void (*bdrv_drain_begin)(BlockDriverState *bs);
> +    void (*bdrv_drain_end)(BlockDriverState *bs);
>  
>      bool (*bdrv_supports_persistent_dirty_bitmap)(BlockDriverState *bs);
>      bool coroutine_fn (*bdrv_co_can_store_new_dirty_bitmap)(
> diff --git a/block.c b/block.c
> index 3bd594eb2a..fed8077993 100644
> --- a/block.c
> +++ b/block.c
> @@ -1705,8 +1705,8 @@ static int bdrv_open_driver(BlockDriverState *bs, 
> BlockDriver *drv,
>      assert(is_power_of_2(bs->bl.request_alignment));
>  
>      for (i = 0; i < bs->quiesce_counter; i++) {
> -        if (drv->bdrv_co_drain_begin) {
> -            drv->bdrv_co_drain_begin(bs);
> +        if (drv->bdrv_drain_begin) {
> +            drv->bdrv_drain_begin(bs);
>          }
>      }
>  
> diff --git a/block/io.c b/block/io.c
> index 34b30e304e..183b407f5b 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -250,55 +250,20 @@ typedef struct {
>      int *drained_end_counter;
>  } BdrvCoDrainData;
>  
> -static void coroutine_fn bdrv_drain_invoke_entry(void *opaque)
> -{
> -    BdrvCoDrainData *data = opaque;
> -    BlockDriverState *bs = data->bs;
> -
> -    if (data->begin) {
> -        bs->drv->bdrv_co_drain_begin(bs);
> -    } else {
> -        bs->drv->bdrv_co_drain_end(bs);
> -    }
> -
> -    /* Set data->done and decrement drained_end_counter before bdrv_wakeup() 
> */
> -    qatomic_mb_set(&data->done, true);
> -    if (!data->begin) {
> -        qatomic_dec(data->drained_end_counter);
> -    }
> -    bdrv_dec_in_flight(bs);
> -
> -    g_free(data);
> -}
> -
> -/* Recursively call BlockDriver.bdrv_co_drain_begin/end callbacks */
> +/* Recursively call BlockDriver.bdrv_drain_begin/end callbacks */
>  static void bdrv_drain_invoke(BlockDriverState *bs, bool begin,
>                                int *drained_end_counter)
>  {
> -    BdrvCoDrainData *data;
> -
> -    if (!bs->drv || (begin && !bs->drv->bdrv_co_drain_begin) ||
> -            (!begin && !bs->drv->bdrv_co_drain_end)) {
> +    if (!bs->drv || (begin && !bs->drv->bdrv_drain_begin) ||
> +            (!begin && !bs->drv->bdrv_drain_end)) {
>          return;
>      }
>  
> -    data = g_new(BdrvCoDrainData, 1);
> -    *data = (BdrvCoDrainData) {
> -        .bs = bs,
> -        .done = false,
> -        .begin = begin,
> -        .drained_end_counter = drained_end_counter,
> -    };
> -
> -    if (!begin) {
> -        qatomic_inc(drained_end_counter);
> +    if (begin) {
> +        bs->drv->bdrv_drain_begin(bs);
> +    } else {
> +        bs->drv->bdrv_drain_end(bs);
>      }
> -
> -    /* Make sure the driver callback completes during the polling phase for
> -     * drain_begin. */
> -    bdrv_inc_in_flight(bs);
> -    data->co = qemu_coroutine_create(bdrv_drain_invoke_entry, data);
> -    aio_co_schedule(bdrv_get_aio_context(bs), data->co);
>  }
>  
>  /* Returns true if BDRV_POLL_WHILE() should go into a blocking aio_poll() */
> diff --git a/block/qed.c b/block/qed.c
> index 013f826c44..301ff8fd86 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -365,7 +365,7 @@ static void bdrv_qed_attach_aio_context(BlockDriverState 
> *bs,
>      }
>  }
>  
> -static void coroutine_fn bdrv_qed_co_drain_begin(BlockDriverState *bs)
> +static void bdrv_qed_co_drain_begin(BlockDriverState *bs)

This function needs to be renamed s/_co_//.

>  {
>      BDRVQEDState *s = bs->opaque;
>  
> @@ -1661,7 +1661,7 @@ static BlockDriver bdrv_qed = {
>      .bdrv_co_check            = bdrv_qed_co_check,
>      .bdrv_detach_aio_context  = bdrv_qed_detach_aio_context,
>      .bdrv_attach_aio_context  = bdrv_qed_attach_aio_context,
> -    .bdrv_co_drain_begin      = bdrv_qed_co_drain_begin,
> +    .bdrv_drain_begin         = bdrv_qed_co_drain_begin,
>  };
>  
>  static void bdrv_qed_init(void)
> diff --git a/block/throttle.c b/block/throttle.c
> index 131eba3ab4..6e3ae1b355 100644
> --- a/block/throttle.c
> +++ b/block/throttle.c
> @@ -214,7 +214,7 @@ static void throttle_reopen_abort(BDRVReopenState 
> *reopen_state)
>      reopen_state->opaque = NULL;
>  }
>  
> -static void coroutine_fn throttle_co_drain_begin(BlockDriverState *bs)
> +static void throttle_co_drain_begin(BlockDriverState *bs)

Same here.

>  {
>      ThrottleGroupMember *tgm = bs->opaque;
>      if (qatomic_fetch_inc(&tgm->io_limits_disabled) == 0) {
> @@ -261,8 +261,8 @@ static BlockDriver bdrv_throttle = {
>      .bdrv_reopen_commit                 =   throttle_reopen_commit,
>      .bdrv_reopen_abort                  =   throttle_reopen_abort,
>  
> -    .bdrv_co_drain_begin                =   throttle_co_drain_begin,
> -    .bdrv_co_drain_end                  =   throttle_co_drain_end,

Is throttle_co_drain_end() still marked coroutine_fn? It also need to be
renamed to throttle_drain_end().

> +    .bdrv_drain_begin                   =   throttle_co_drain_begin,
> +    .bdrv_drain_end                     =   throttle_co_drain_end,
>  
>      .is_filter                          =   true,
>      .strong_runtime_opts                =   throttle_strong_runtime_opts,
> diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
> index 24f34e24ad..695519ee02 100644
> --- a/tests/unit/test-bdrv-drain.c
> +++ b/tests/unit/test-bdrv-drain.c
> @@ -46,7 +46,7 @@ static void coroutine_fn sleep_in_drain_begin(void *opaque)
>      bdrv_dec_in_flight(bs);
>  }
>  
> -static void coroutine_fn bdrv_test_co_drain_begin(BlockDriverState *bs)
> +static void bdrv_test_drain_begin(BlockDriverState *bs)
>  {
>      BDRVTestState *s = bs->opaque;
>      s->drain_count++;
> @@ -57,7 +57,7 @@ static void coroutine_fn 
> bdrv_test_co_drain_begin(BlockDriverState *bs)
>      }
>  }
>  
> -static void coroutine_fn bdrv_test_co_drain_end(BlockDriverState *bs)
> +static void bdrv_test_drain_end(BlockDriverState *bs)
>  {
>      BDRVTestState *s = bs->opaque;
>      s->drain_count--;
> @@ -111,8 +111,8 @@ static BlockDriver bdrv_test = {
>      .bdrv_close             = bdrv_test_close,
>      .bdrv_co_preadv         = bdrv_test_co_preadv,
>  
> -    .bdrv_co_drain_begin    = bdrv_test_co_drain_begin,
> -    .bdrv_co_drain_end      = bdrv_test_co_drain_end,
> +    .bdrv_drain_begin       = bdrv_test_drain_begin,
> +    .bdrv_drain_end         = bdrv_test_drain_end,
>  
>      .bdrv_child_perm        = bdrv_default_perms,
>  
> @@ -1703,6 +1703,7 @@ static void test_blockjob_commit_by_drained_end(void)
>      bdrv_drained_begin(bs_child);
>      g_assert(!job_has_completed);
>      bdrv_drained_end(bs_child);
> +    aio_poll(qemu_get_aio_context(), false);
>      g_assert(job_has_completed);
>  
>      bdrv_unref(bs_parents[0]);
> @@ -1858,6 +1859,7 @@ static void test_drop_intermediate_poll(void)
>  
>      g_assert(!job_has_completed);
>      ret = bdrv_drop_intermediate(chain[1], chain[0], NULL);
> +    aio_poll(qemu_get_aio_context(), false);
>      g_assert(ret == 0);
>      g_assert(job_has_completed);
>  
> @@ -1946,7 +1948,7 @@ static void coroutine_fn 
> bdrv_replace_test_drain_co(void *opaque)
>   * .was_drained.
>   * Increment .drain_count.
>   */
> -static void coroutine_fn bdrv_replace_test_co_drain_begin(BlockDriverState 
> *bs)
> +static void bdrv_replace_test_drain_begin(BlockDriverState *bs)
>  {
>      BDRVReplaceTestState *s = bs->opaque;
>  
> @@ -1977,7 +1979,7 @@ static void coroutine_fn 
> bdrv_replace_test_read_entry(void *opaque)
>   * If .drain_count reaches 0 and the node has a backing file, issue a
>   * read request.
>   */
> -static void coroutine_fn bdrv_replace_test_co_drain_end(BlockDriverState *bs)
> +static void bdrv_replace_test_drain_end(BlockDriverState *bs)
>  {
>      BDRVReplaceTestState *s = bs->opaque;
>  
> @@ -2002,8 +2004,8 @@ static BlockDriver bdrv_replace_test = {
>      .bdrv_close             = bdrv_replace_test_close,
>      .bdrv_co_preadv         = bdrv_replace_test_co_preadv,
>  
> -    .bdrv_co_drain_begin    = bdrv_replace_test_co_drain_begin,
> -    .bdrv_co_drain_end      = bdrv_replace_test_co_drain_end,
> +    .bdrv_drain_begin       = bdrv_replace_test_drain_begin,
> +    .bdrv_drain_end         = bdrv_replace_test_drain_end,
>  
>      .bdrv_child_perm        = bdrv_default_perms,
>  };
> -- 
> 2.38.1
>

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