bcache: fix oops bug in cache_set_flush

[liequan che]

Signed-off-by: cheliequan <cheliequan@xxxxxxxxxx>

   If the bcache cache disk contains damaged btree data,
when the bcache cache disk partition is directly operated,
the system-udevd service is triggered to call the bcache-register
program to register the bcache device,resulting in kernel oops.

crash> bt
PID: 7773     TASK: ffff49cc44d69340  CPU: 57   COMMAND: "kworker/57:2"
 #0 [ffff800046373800] machine_kexec at ffffbe5039eb54a8
 #1 [ffff8000463739b0] __crash_kexec at ffffbe503a052824
 #2 [ffff8000463739e0] crash_kexec at ffffbe503a0529cc
 #3 [ffff800046373a60] die at ffffbe5039e9445c
 #4 [ffff800046373ac0] die_kernel_fault at ffffbe5039ec698c
 #5 [ffff800046373af0] __do_kernel_fault at ffffbe5039ec6a38
 #6 [ffff800046373b20] do_page_fault at ffffbe503ac76ba4
 #7 [ffff800046373b70] do_translation_fault at ffffbe503ac76ebc
 #8 [ffff800046373b90] do_mem_abort at ffffbe5039ec68ac
 #9 [ffff800046373bc0] el1_abort at ffffbe503ac669bc
#10 [ffff800046373bf0] el1_sync_handler at ffffbe503ac671d4
#11 [ffff800046373d30] el1_sync at ffffbe5039e82230
#12 [ffff800046373d50] cache_set_flush at ffffbe50121fa4c4 [bcache]
#13 [ffff800046373da0] process_one_work at ffffbe5039f5af68
#14 [ffff800046373e00] worker_thread at ffffbe5039f5b3c4
#15 [ffff800046373e50] kthread at ffffbe5039f634b8
crash> dis cache_set_flush+0x94
0xffffbe50121fa4c8 <cache_set_flush+148>:       str     x23, [x20, #512]

---
drivers/md/bcache/super.c | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index fd97730479d8..8a41dfcf9fb6 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1741,8 +1741,10 @@ static void cache_set_flush(struct closure *cl)
       if (!IS_ERR_OR_NULL(c->gc_thread))
               kthread_stop(c->gc_thread);

-       if (!IS_ERR(c->root))
-               list_add(&c->root->list, &c->btree_cache);
+       if (!IS_ERR_OR_NULL(c->root)) {
+               if (!list_empty(&c->root->list))
+                       list_add(&c->root->list, &c->btree_cache);
+       }

       /*
        * Avoid flushing cached nodes if cache set is retiring
@@ -1750,10 +1752,12 @@ static void cache_set_flush(struct closure *cl)
        */
       if (!test_bit(CACHE_SET_IO_DISABLE, &c->flags))
               list_for_each_entry(b, &c->btree_cache, list) {
-                       mutex_lock(&b->write_lock);
-                       if (btree_node_dirty(b))
-                               __bch_btree_node_write(b, NULL);
-                       mutex_unlock(&b->write_lock);
+                       if (!IS_ERR_OR_NULL(b)) {
+                               mutex_lock(&b->write_lock);
+                               if (btree_node_dirty(b))
+                                       __bch_btree_node_write(b, NULL);
+                               mutex_unlock(&b->write_lock);
+                       }
               }

       if (ca->alloc_thread)
--
2.33.0