ext4: use RCU API in debug_print_tree

struct ext4_sb_info.system_blks was marked __rcu.
But access the pointer without using RCU lock and dereference.
Sparse warning with __rcu notation:

block_validity.c:139:29: warning: incorrect type in argument 1 (different address spaces)
block_validity.c:139:29:    expected struct rb_root const *
block_validity.c:139:29:    got struct rb_root [noderef] <asn:4> *

Link: https://lore.kernel.org/r/20191213153306.30744-1-tranmanphong@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Phong Tran <tranmanphong@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index d4d4fdf..1ee04e7 100644 (file)
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -133,10 +133,13 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
 {
        struct rb_node *node;
        struct ext4_system_zone *entry;
+       struct ext4_system_blocks *system_blks;
        int first = 1;
 
        printk(KERN_INFO "System zones: ");
-       node = rb_first(&sbi->system_blks->root);
+       rcu_read_lock();
+       system_blks = rcu_dereference(sbi->system_blks);
+       node = rb_first(&system_blks->root);
        while (node) {
                entry = rb_entry(node, struct ext4_system_zone, node);
                printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ",
@@ -144,6 +147,7 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
                first = 0;
                node = rb_next(node);
        }
+       rcu_read_unlock();
        printk(KERN_CONT "\n");
 }