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SubjectRe: [PATCH V2] ext4: use rcu API in debug_print_tree
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.

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

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