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block: move drain outside of bdrv_set_backing_hd_drained()

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This is part of resolving the deadlock mentioned in commit "block:
move draining out of bdrv_change_aio_context() and mark GRAPH_RDLOCK".

The function bdrv_set_backing_hd_drained() holds the graph lock, so it
is not allowed to drain. It is called by:
1. bdrv_set_backing_hd(), where a drained section is introduced,
   replacing the previously present bs-specific drains.
2. stream_prepare(), where a drained section is introduced replacing
   the previously present bs-specific drains.

The drain_bs variable in bdrv_set_backing_hd_drained() is now
superfluous and thus dropped.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250530151125.955508-12-f.ebner@proxmox.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fiona Ebner 2025-05-30 17:10:48 +02:00 • committed by Kevin Wolf
parent 2b833595aa
commit e66dbda11e
2 changed files with 5 additions and 17 deletions
Download patch file Download diff file Expand all files Collapse all files

16
block.c
View file

@ -3562,8 +3562,7 @@ out:
* Both @bs and @backing_hd can move to a different AioContext in this
* function.
*
* If a backing child is already present (i.e. we're detaching a node), that
* child node must be drained.
* All block nodes must be drained.
*/
int bdrv_set_backing_hd_drained(BlockDriverState *bs,
BlockDriverState *backing_hd,
@ -3578,7 +3577,6 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs,
assert(bs->backing->bs->quiesce_counter > 0);
}
bdrv_drain_all_begin();
ret = bdrv_set_file_or_backing_noperm(bs, backing_hd, true, tran, errp);
if (ret < 0) {
goto out;
@ -3587,28 +3585,20 @@ int bdrv_set_backing_hd_drained(BlockDriverState *bs,
ret = bdrv_refresh_perms(bs, tran, errp);
out:
tran_finalize(tran, ret);
bdrv_drain_all_end();
return ret;
}
int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
Error **errp)
{
BlockDriverState *drain_bs;
int ret;
GLOBAL_STATE_CODE();
bdrv_graph_rdlock_main_loop();
drain_bs = bs->backing ? bs->backing->bs : bs;
bdrv_graph_rdunlock_main_loop();
bdrv_ref(drain_bs);
bdrv_drained_begin(drain_bs);
bdrv_drain_all_begin();
bdrv_graph_wrlock();
ret = bdrv_set_backing_hd_drained(bs, backing_hd, errp);
bdrv_graph_wrunlock();
bdrv_drained_end(drain_bs);
bdrv_unref(drain_bs);
bdrv_drain_all_end();
return ret;
}

6
block/stream.c
View file

@ -80,11 +80,10 @@ static int stream_prepare(Job *job)
* may end up working with the wrong base node (or it might even have gone
* away by the time we want to use it).
*/
bdrv_drained_begin(unfiltered_bs);
if (unfiltered_bs_cow) {
bdrv_ref(unfiltered_bs_cow);
bdrv_drained_begin(unfiltered_bs_cow);
}
bdrv_drain_all_begin();
bdrv_graph_rdlock_main_loop();
base = bdrv_filter_or_cow_bs(s->above_base);
@ -123,11 +122,10 @@ static int stream_prepare(Job *job)
}
out:
bdrv_drain_all_end();
if (unfiltered_bs_cow) {
bdrv_drained_end(unfiltered_bs_cow);
bdrv_unref(unfiltered_bs_cow);
}
bdrv_drained_end(unfiltered_bs);
return ret;
}