diff mbox series

[V2] ext4: use rcu API in debug_print_tree

Message ID 20191213153306.30744-1-tranmanphong@gmail.com
State Accepted
Headers show
Series [V2] ext4: use rcu API in debug_print_tree | expand

Commit Message

Phong Tran Dec. 13, 2019, 3:33 p.m. UTC 
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>
---
 fs/ext4/block_validity.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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

Comments

Joel Fernandes Dec. 13, 2019, 6:11 p.m. UTC | #1 
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?

- 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 Dec. 13, 2019, 7:49 p.m. UTC | #2 
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
> >
Joel Fernandes Dec. 13, 2019, 11:19 p.m. UTC | #3 
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
Theodore Ts'o Dec. 16, 2019, 2:41 a.m. UTC | #4 
On Fri, Dec 13, 2019 at 10:33:07PM +0700, Phong Tran 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>

Applied, thanks.

						- Ted
diff mbox series

Patch

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");
 }