merge spa from upstream (openzfs#123)

* Avoid dirtying the final TXGs when exporting a pool

There are two codepaths than can dirty final TXGs:

1) If calling spa_export_common()->spa_unload()->
   spa_unload_log_sm_flush_all() after the spa_final_txg is set, then
   spa_sync()->spa_flush_metaslabs() may end up dirtying the final
   TXGs. Then we have the following panic:
   Call Trace:
    <TASK>
    dump_stack_lvl+0x46/0x62
    spl_panic+0xea/0x102 [spl]
    dbuf_dirty+0xcd6/0x11b0 [zfs]
    zap_lockdir_impl+0x321/0x590 [zfs]
    zap_lockdir+0xed/0x150 [zfs]
    zap_update+0x69/0x250 [zfs]
    feature_sync+0x5f/0x190 [zfs]
    space_map_alloc+0x83/0xc0 [zfs]
    spa_generate_syncing_log_sm+0x10b/0x2f0 [zfs]
    spa_flush_metaslabs+0xb2/0x350 [zfs]
    spa_sync_iterate_to_convergence+0x15a/0x320 [zfs]
    spa_sync+0x2e0/0x840 [zfs]
    txg_sync_thread+0x2b1/0x3f0 [zfs]
    thread_generic_wrapper+0x62/0xa0 [spl]
    kthread+0x127/0x150
    ret_from_fork+0x22/0x30
    </TASK>

2) Calling vdev_*_stop_all() for a second time in spa_unload() after
   spa_export_common() unnecessarily delays the final TXGs beyond what
   spa_final_txg is set at.

Fix this by performing the check and call for
spa_unload_log_sm_flush_all() before the spa_final_txg is set in
spa_export_common(). Also check if the spa_final_txg has already been
set in spa_unload() and skip those calls in this case.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
External-issue: https://www.illumos.org/issues/9081
Closes openzfs#13048 
Closes openzfs#13098

* Add spa _os() hooks

Add hooks for when spa is created, exported, activated and
deactivated. Used by macOS to attach iokit, and lock
kext as busy (to stop unloads).

Userland, Linux, and, FreeBSD have empty stubs.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Jorgen Lundman <lundman@lundman.net>
Closes openzfs#12801

* Windows: Add spa_os() hooks

use the common spa prototypes instead of the windows specific ones

Signed-off-by: Andrew Innes <andrew.c12@gmail.com>

Signed-off-by: Andrew Innes <andrew.c12@gmail.com>
Co-authored-by: George Amanakis <gamanakis@gmail.com>
Co-authored-by: Jorgen Lundman <lundman@lundman.net>

include/os/windows/zfs/sys/zfs_context_os.h

@@ -195,10 +195,6 @@ extern void kx_qsort(void *array, size_t nm, size_t member_size,
 
 #define	strstr kmem_strstr
 
-void spa_create_os(void *spa);
-void spa_export_os(void *spa);
-void spa_activate_os(void *spa);
-void spa_deactivate_os(void *spa);
 
 #define	task_io_account_read(n)
 #define	task_io_account_write(n)

module/os/windows/zfs/spa_misc_os.c

@@ -54,23 +54,23 @@ spa_history_zone(void)
 }
 
 void
-spa_create_os(void *arg)
+spa_import_os(spa_t *arg)
 {
 }
 
 void
-spa_export_os(void *arg)
+spa_export_os(spa_t *arg)
 {
 }
 
 void
-spa_activate_os(void *arg)
+spa_activate_os(spa_t *arg)
 {
 	atomic_inc_64(&zfs_module_busy);
 }
 
 void
-spa_deactivate_os(void *arg)
+spa_deactivate_os(spa_t *arg)
 {
 	atomic_dec_64(&zfs_module_busy);
 }