block: Convert bdrv_refresh_total_sectors() to co_wrapper_mixed

BlockDriver->bdrv_getlength is categorized as IO callback, and it
currently doesn't run in a coroutine. We should let it take a graph
rdlock since the callback traverses the block nodes graph, which however
is only possible in a coroutine.

Therefore turn it into a co_wrapper to move the actual function into a
coroutine where the lock can be taken.

Because now this function creates a new coroutine and polls, we need to
take the AioContext lock where it is missing, for the only reason that
internally co_wrapper calls AIO_WAIT_WHILE and it expects to release the
AioContext lock.

This is especially messy when a co_wrapper creates a coroutine and polls
in bdrv_open_driver, because this function has so many callers in so
many context that it can easily lead to deadlocks. Therefore the new
rule for bdrv_open_driver is that the caller must always hold the
AioContext lock of the given bs (except if it is a coroutine), because
the function calls bdrv_refresh_total_sectors() which is now a
co_wrapper.

Once the rwlock is ultimated and placed in every place it needs to be,
we will poll using AIO_WAIT_WHILE_UNLOCKED and remove the AioContext
lock.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230113204212.359076-7-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

4 files changed, 19 insertions, 6 deletions

diff --git a/include/block/block-io.h b/include/block/block-io.h
index f27d935982..dcb6270f77 100644
--- a/include/block/block-io.h
+++ b/include/block/block-io.h
@@ -76,8 +76,12 @@ int coroutine_fn bdrv_co_truncate(BdrvChild *child, int64_t offset, bool exact,
                                   PreallocMode prealloc, BdrvRequestFlags flags,
                                   Error **errp);
 
-int64_t bdrv_nb_sectors(BlockDriverState *bs);
-int64_t bdrv_getlength(BlockDriverState *bs);
+int64_t coroutine_fn bdrv_co_nb_sectors(BlockDriverState *bs);
+int64_t co_wrapper_mixed bdrv_nb_sectors(BlockDriverState *bs);
+
+int64_t coroutine_fn bdrv_co_getlength(BlockDriverState *bs);
+int64_t co_wrapper_mixed bdrv_getlength(BlockDriverState *bs);
+
 int64_t bdrv_get_allocated_file_size(BlockDriverState *bs);
 BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts,
                                BlockDriverState *in_bs, Error **errp);
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 9ec68f515c..5381681fbc 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -680,7 +680,7 @@ struct BlockDriver {
     int coroutine_fn (*bdrv_co_truncate)(BlockDriverState *bs, int64_t offset,
                                          bool exact, PreallocMode prealloc,
                                          BdrvRequestFlags flags, Error **errp);
-    int64_t (*bdrv_getlength)(BlockDriverState *bs);
+    int64_t coroutine_fn (*bdrv_co_getlength)(BlockDriverState *bs);
     int64_t (*bdrv_get_allocated_file_size)(BlockDriverState *bs);
     BlockMeasureInfo *(*bdrv_measure)(QemuOpts *opts, BlockDriverState *in_bs,
                                       Error **errp);
diff --git a/include/block/block_int-io.h b/include/block/block_int-io.h
index 37b0fd974b..4430bf4c4a 100644
--- a/include/block/block_int-io.h
+++ b/include/block/block_int-io.h
@@ -122,7 +122,10 @@ int coroutine_fn bdrv_co_copy_range_to(BdrvChild *src, int64_t src_offset,
                                        BdrvRequestFlags read_flags,
                                        BdrvRequestFlags write_flags);
 
-int bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint);
+int coroutine_fn bdrv_co_refresh_total_sectors(BlockDriverState *bs,
+                                               int64_t hint);
+int co_wrapper_mixed
+bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint);
 
 BdrvChild *bdrv_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_child(BlockDriverState *bs);
diff --git a/include/sysemu/block-backend-io.h b/include/sysemu/block-backend-io.h
index 7cc96a56c7..ce013b3312 100644
--- a/include/sysemu/block-backend-io.h
+++ b/include/sysemu/block-backend-io.h
@@ -61,9 +61,15 @@ bool co_wrapper_mixed blk_is_inserted(BlockBackend *blk);
 bool blk_is_available(BlockBackend *blk);
 void blk_lock_medium(BlockBackend *blk, bool locked);
 void blk_eject(BlockBackend *blk, bool eject_flag);
-int64_t blk_getlength(BlockBackend *blk);
+
+int64_t coroutine_fn blk_co_getlength(BlockBackend *blk);
+int64_t co_wrapper_mixed blk_getlength(BlockBackend *blk);
+
 void blk_get_geometry(BlockBackend *blk, uint64_t *nb_sectors_ptr);
-int64_t blk_nb_sectors(BlockBackend *blk);
+
+int64_t coroutine_fn blk_co_nb_sectors(BlockBackend *blk);
+int64_t co_wrapper_mixed blk_nb_sectors(BlockBackend *blk);
+
 void *blk_try_blockalign(BlockBackend *blk, size_t size);
 void *blk_blockalign(BlockBackend *blk, size_t size);
 bool blk_is_writable(BlockBackend *blk);