kgdb: Don't call the deinit under spinlock

When I combined kgdboc_earlycon with an inflight patch titled ("soc:
qcom-geni-se: Add interconnect support to fix earlycon crash") [1]
things went boom.  Specifically I got a crash during the transition
between kgdboc_earlycon and the main kgdboc that looked like this:

Call trace:
 __schedule_bug+0x68/0x6c
 __schedule+0x75c/0x924
 schedule+0x8c/0xbc
 schedule_timeout+0x9c/0xfc
 do_wait_for_common+0xd0/0x160
 wait_for_completion_timeout+0x54/0x74
 rpmh_write_batch+0x1fc/0x23c
 qcom_icc_bcm_voter_commit+0x1b4/0x388
 qcom_icc_set+0x2c/0x3c
 apply_constraints+0x5c/0x98
 icc_set_bw+0x204/0x3bc
 icc_put+0x30/0xf8
 geni_remove_earlycon_icc_vote+0x6c/0x9c
 qcom_geni_serial_earlycon_exit+0x10/0x1c
 kgdboc_earlycon_deinit+0x38/0x58
 kgdb_register_io_module+0x11c/0x194
 configure_kgdboc+0x108/0x174
 kgdboc_probe+0x38/0x60
 platform_drv_probe+0x90/0xb0
 really_probe+0x130/0x2fc
 ...

The problem was that we were holding the "kgdb_registration_lock"
while calling into code that didn't expect to be called in spinlock
context.

Let's slightly defer when we call the deinit code so that it's not
done under spinlock.

NOTE: this does mean that the "deinit" call of the old kgdb IO module
is now made _after_ the init of the new IO module, but presumably
that's OK.

[1] https://lkml.kernel.org/r/[email protected]

Fixes: 2209956 ("kgdboc: Add kgdboc_earlycon to support early kgdb using boot consoles")
Signed-off-by: Douglas Anderson <[email protected]>
Link: https://lore.kernel.org/r/20200526142001.1.I523dc33f96589cb9956f5679976d402c8cda36fa@changeid
[[email protected]: Resolved merge issues by hand]
Signed-off-by: Daniel Thompson <[email protected]>

Author: dianders

kernel/debug/debug_core.c

@@ -1089,7 +1089,6 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 		}
 		pr_info("Replacing I/O driver %s with %s\n",
 			old_dbg_io_ops->name, new_dbg_io_ops->name);
-		old_dbg_io_ops->deinit();
 	}
 
 	if (new_dbg_io_ops->init) {
@@ -1104,8 +1103,10 @@ int kgdb_register_io_module(struct kgdb_io *new_dbg_io_ops)
 
 	spin_unlock(&kgdb_registration_lock);
 
-	if (old_dbg_io_ops)
+	if (old_dbg_io_ops) {
+		old_dbg_io_ops->deinit();
 		return 0;
+	}
 
 	pr_info("Registered I/O driver %s\n", new_dbg_io_ops->name);