Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity

["Theodore Y. Ts'o" <tytso@xxxxxxx>]

I added a missing rcu_read_lock() to prevent a suspicious RCU
warning when CONFIG_PROVE_RCU is enabled:

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index 003dc1dc2da3..f7bc914a74df 100644
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -330,11 +330,13 @@ void ext4_release_system_zone(struct super_block *sb)
 {
 	struct ext4_system_blocks *system_blks;
 
+	rcu_read_lock();
 	system_blks = rcu_dereference(EXT4_SB(sb)->system_blks);
 	rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);
 
 	if (system_blks)
 		call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
+	rcu_read_unlock();
 }
 
 int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,


     				  	       	     - Ted