On Wed, Oct 21, 2015 at 10:06:48AM +0800, Fam Zheng wrote:
> The "need_check_timer" is used to clear the "NEED_CHECK" flag in the
> image header after a grace period once metadata update has finished. In
> compliance to the bdrv_drain semantics we should make sure it remains
> deleted once .bdrv_drain is called.
>
> Call the qed_need_check_timer_cb manually to update the header
> immediately.
>
> Signed-off-by: Fam Zheng <[email protected]>
> ---
> block/qed.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/block/qed.c b/block/qed.c
> index 5ea05d4..e9dcb4d 100644
> --- a/block/qed.c
> +++ b/block/qed.c
> @@ -375,6 +375,12 @@ static void bdrv_qed_attach_aio_context(BlockDriverState
> *bs,
> }
> }
>
> +static void bdrv_qed_drain(BlockDriverState *bs)
> +{
> + qed_cancel_need_check_timer(bs->opaque);
> + qed_need_check_timer_cb(bs->opaque);
> +}
> +
Uh oh.
This causes a segfault sometimes, and other times an abort:
# ./qemu-img create -f qed test.qed 512M
Formatting 'test.qed', fmt=qed size=536870912 cluster_size=65536
# ./qemu-io -c "read 0 512M" test.qed
read 536870912/536870912 bytes at offset 0
512 MiB, 1 ops; 0.0556 sec (8.988 GiB/sec and 17.9759 ops/sec)
Segmentation fault (core dumped)
If I run the above qemu-io command with gdb, it will abort in
qed_plug_allocating_write_reqs().
I'd hazard a guess (I have not verified) that it is due to the
qed_header_write() call triggered by the aio flush callback function
qed_clear_need_check(). The aio flush is done inside the
qed_need_check_timer_cb() call.
> static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
> Error **errp)
> {
> @@ -1676,6 +1682,7 @@ static BlockDriver bdrv_qed = {
> .bdrv_check = bdrv_qed_check,
> .bdrv_detach_aio_context = bdrv_qed_detach_aio_context,
> .bdrv_attach_aio_context = bdrv_qed_attach_aio_context,
> + .bdrv_drain = bdrv_qed_drain,
> };
>
> static void bdrv_qed_init(void)
> --
> 2.4.3
>
>
