md: Don't flush sync_work in md_write_start()

Because flush sync_work may trigger mddev_suspend() if there are spares,
and this should never be done in IO path because mddev_suspend() is used
to wait for IO.

This problem is found by code review.

Fixes: bc08041 ("md: suspend array in md_start_sync() if array need reconfiguration")
Cc: stable@vger.kernel.org
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20240801124746.242558-1-yukuai1@huaweicloud.com
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/md.c

@@ -8668,7 +8668,6 @@ void md_write_start(struct mddev *mddev, struct bio *bi)
 	BUG_ON(mddev->ro == MD_RDONLY);
 	if (mddev->ro == MD_AUTO_READ) {
 		/* need to switch to read/write */
-		flush_work(&mddev->sync_work);
 		mddev->ro = MD_RDWR;
 		set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 		md_wakeup_thread(mddev->thread);