2019-12-01 03:52:13

by Phong Tran

Subject: [PATCH] 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> *

Signed-off-by: Phong Tran <[email protected]>
---
fs/ext4/block_validity.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

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

2019-12-13 11:35:25

by Jan Kara

Subject: Re: [PATCH] ext4: use rcu API in debug_print_tree

On Sun 01-12-19 10:51:07, 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> *
>
> Signed-off-by: Phong Tran <[email protected]>

Thanks for the patch. It looks good to me. You can add:

Reviewed-by: Jan Kara <[email protected]>

Honza

> ---
> fs/ext4/block_validity.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> 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 <[email protected]>
SUSE Labs, CR

2019-12-13 15:40:07

by Phong Tran

Subject: [PATCH V2] 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> *

Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Phong Tran <[email protected]>
---
fs/ext4/block_validity.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

---
change log:
V2: Add Reviewed-by: Jan Kara <[email protected]>

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

2019-12-13 18:12:27

by Joel Fernandes

Subject: Re: [PATCH V2] ext4: use rcu API in debug_print_tree

On Fri, Dec 13, 2019 at 7:39 AM Phong Tran <[email protected]> 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 <[email protected]>
> Signed-off-by: Phong Tran <[email protected]>

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 <[email protected]>
>
> 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
>

2019-12-13 19:50:50

by Jan Kara

Subject: Re: [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 <[email protected]> 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 <[email protected]>
> > Signed-off-by: Phong Tran <[email protected]>
>
> 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 <[email protected]>
> >
> > 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 <[email protected]>
SUSE Labs, CR

2019-12-13 23:20:02

by Joel Fernandes

Subject: Re: [PATCH V2] ext4: use rcu API in debug_print_tree

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 <[email protected]> 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 <[email protected]>
> > > Signed-off-by: Phong Tran <[email protected]>
> >
> > 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 <[email protected]>
> > >
> > > 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 <[email protected]>
> SUSE Labs, CR