devlink: hold region lock when flushing snapshots

In the Linux kernel, the following vulnerability has been resolved:

devlink: hold region lock when flushing snapshots

Netdevsim triggers a splat on reload, when it destroys regions

with snapshots pending:

WARNING: CPU: 1 PID: 787 at net/core/devlink.c:6291 devlink_region_snapshot_del+0x12e/0x140

CPU: 1 PID: 787 Comm: devlink Not tainted 6.1.0-07460-g7ae9888d6e1c #580

RIP: 0010:devlink_region_snapshot_del+0x12e/0x140

Call Trace:

<TASK>

devl_region_destroy+0x70/0x140

nsim_dev_reload_down+0x2f/0x60 [netdevsim]

devlink_reload+0x1f7/0x360

devlink_nl_cmd_reload+0x6ce/0x860

genl_family_rcv_msg_doit.isra.0+0x145/0x1c0

This is the locking assert in devlink_region_snapshot_del(),

we're supposed to be holding the region->snapshot_lock here.