Fix deadlock on dmu_tx_assign() from vdev_rebuild()

vdev_rebuild() is always called with spa_config_lock held in
RW_WRITER mode. However, when it tries to call dmu_tx_assign()
the latter may hang on dmu_tx_wait() waiting for available txg.
But that available txg may not happen because txg_sync takes
spa_config_lock in order to process the current txg. So we have
a deadlock case here:

 - dmu_tx_assign() waits for txg holding spa_config_lock;
 - txg_sync waits for spa_config_lock not progressing with txg.

Here are the stacks:

    __schedule+0x24e/0x590
    schedule+0x69/0x110
    cv_wait_common+0xf8/0x130 [spl]
    __cv_wait+0x15/0x20 [spl]
    dmu_tx_wait+0x8e/0x1e0 [zfs]
    dmu_tx_assign+0x49/0x80 [zfs]
    vdev_rebuild_initiate+0x39/0xc0 [zfs]
    vdev_rebuild+0x84/0x90 [zfs]
    spa_vdev_attach+0x305/0x680 [zfs]
    zfs_ioc_vdev_attach+0xc7/0xe0 [zfs]

    cv_wait_common+0xf8/0x130 [spl]
    __cv_wait+0x15/0x20 [spl]
    spa_config_enter+0xf9/0x120 [zfs]
    spa_sync+0x6d/0x5b0 [zfs]
    txg_sync_thread+0x266/0x2f0 [zfs]

The solution is to pass txg returned by spa_vdev_enter(spa)
at the top of spa_vdev_attach() to vdev_rebuild() and call
dmu_tx_create_assigned(txg) which doesn't wait for txg.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Akash B <akash-b@hpe.com>
Reviewed-by: Alek Pinchuk <apinchuk@axcient.com>
Signed-off-by: Andriy Tkachuk <andriy.tkachuk@seagate.com>
Closes #18210
Closes #18258

include/sys/vdev_rebuild.h

@@ -90,7 +90,7 @@ typedef struct vdev_rebuild {
 boolean_t vdev_rebuild_active(vdev_t *);
 
 int vdev_rebuild_load(vdev_t *);
-void vdev_rebuild(vdev_t *);
+void vdev_rebuild(vdev_t *, uint64_t);
 void vdev_rebuild_stop_wait(vdev_t *);
 void vdev_rebuild_stop_all(spa_t *);
 void vdev_rebuild_restart(spa_t *);