On Fri, Dec 13, 2019 at 08:49:43PM +0100, Jan Kara wrote:

On Fri 13-12-19 10:11:50, Joel Fernandes wrote:

...

On Fri, Dec 13, 2019 at 7:39 AM Phong Tran tranmanphong@gmail.com wrote:

...

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 *

Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Phong Tran tranmanphong@gmail.com

Thanks Phong! Looks like a real bug fix caught thanks to Sparse. So let us mark for stable as well?

Well, not really. The code is active only with CONFIG_EXT4_DEBUG enabled and in this case there's no race with remount (and thus sbi->system_blks changing) possible. So the change is really only to silence the sparse warning.

Ok, thanks for clarifying.

-Joel

						Honza

...

• Joel

...

---

fs/ext4/block_validity.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

---

change log: V2: Add Reviewed-by: Jan Kara jack@suse.cz

diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c index d4d4fdfac1a6..1ee04e76bbe0 100644 --- 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");
  

}

-- 2.20.1

-- Jan Kara jack@suse.com SUSE Labs, CR