[PATCH v1] qmp: don't hold ctx lock while querying blockstats

[Zhenyu Ye]

Because the QMP command runs in the main thread, and changes
to the aio context of iothread will only be executed in the
main thread (they will not be in parallel), so there is no
need a lock protection while querying blockstats.

If we hold the lock here, while the I/O pressure is high in
vm and the I/O returns slowly, the main thread will be stuck
until the lock is released, which will affect the vcpu operation
and finall cause the vm to be stuck.

Signed-off-by: Zhenyu Ye <yezhenyu2@huawei.com>
---
 block/qapi.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/block/qapi.c b/block/qapi.c
index afd9f3b4a7..fa56bc145d 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -609,11 +609,8 @@ BlockStatsList *qmp_query_blockstats(bool has_query_nodes,
     if (has_query_nodes && query_nodes) {
         for (bs = bdrv_next_node(NULL); bs; bs = bdrv_next_node(bs)) {
             BlockStatsList *info = g_malloc0(sizeof(*info));
-            AioContext *ctx = bdrv_get_aio_context(bs);
 
-            aio_context_acquire(ctx);
             info->value = bdrv_query_bds_stats(bs, false);
-            aio_context_release(ctx);
 
             *p_next = info;
             p_next = &info->next;
@@ -621,7 +618,6 @@ BlockStatsList *qmp_query_blockstats(bool has_query_nodes,
     } else {
         for (blk = blk_all_next(NULL); blk; blk = blk_all_next(blk)) {
             BlockStatsList *info;
-            AioContext *ctx = blk_get_aio_context(blk);
             BlockStats *s;
             char *qdev;
 
@@ -629,7 +625,6 @@ BlockStatsList *qmp_query_blockstats(bool has_query_nodes,
                 continue;
             }
 
-            aio_context_acquire(ctx);
             s = bdrv_query_bds_stats(blk_bs(blk), true);
             s->has_device = true;
             s->device = g_strdup(blk_name(blk));
@@ -643,7 +638,6 @@ BlockStatsList *qmp_query_blockstats(bool has_query_nodes,
             }
 
             bdrv_query_blk_stats(s->stats, blk);
-            aio_context_release(ctx);
 
             info = g_malloc0(sizeof(*info));
             info->value = s;
-- 
2.19.1