Fix ARC aggsum access after arc_state_fini()

Commit 85ec5cbae updated abd_update_scatter_stats() such that it
calls arc_space_consume() and arc_space_return() when updating the
scatter stats.  This requires that the global aggsum value for the
ARC be initialized.  Normally this is not an issue, however during
module unload the l2arc_do_free_on_write() function was called in
l2arc_cleanup() after arc_state_fini() destroyed the aggsum values.
We can resolve this issue by performing l2arc_do_free_on_write()
slightly earlier in arc_fini().

Reviewed-by: Matthew Ahrens <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #10739 

1 files changed, 8 insertions, 8 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index f63f92b86..0512497d5 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -886,6 +886,7 @@ static inline void arc_hdr_clear_flags(arc_buf_hdr_t *hdr, arc_flags_t flags);
 
 static boolean_t l2arc_write_eligible(uint64_t, arc_buf_hdr_t *);
 static void l2arc_read_done(zio_t *);
+static void l2arc_do_free_on_write(void);
 
 /*
  * L2ARC TRIM
@@ -7555,6 +7556,13 @@ arc_fini(void)
 	list_destroy(&arc_evict_waiters);
 
 	/*
+	 * Free any buffers that were tagged for destruction.  This needs
+	 * to occur before arc_state_fini() runs and destroys the aggsum
+	 * values which are updated when freeing scatter ABDs.
+	 */
+	l2arc_do_free_on_write();
+
+	/*
 	 * buf_fini() must proceed arc_state_fini() because buf_fin() may
 	 * trigger the release of kmem magazines, which can callback to
 	 * arc_space_return() which accesses aggsums freed in act_state_fini().
@@ -9451,14 +9459,6 @@ l2arc_init(void)
 void
 l2arc_fini(void)
 {
-	/*
-	 * This is called from dmu_fini(), which is called from spa_fini();
-	 * Because of this, we can assume that all l2arc devices have
-	 * already been removed when the pools themselves were removed.
-	 */
-
-	l2arc_do_free_on_write();
-
 	mutex_destroy(&l2arc_feed_thr_lock);
 	cv_destroy(&l2arc_feed_thr_cv);
 	mutex_destroy(&l2arc_rebuild_thr_lock);