Remount process will release system zone which was allocated before if
"noblock_validity" is specified. If we mount an ext4 file system to two
mountpoints with default mount options, and then remount one of them
with "noblock_validity", it may trigger a use after free problem when
someone accessing the other one.
# mount /dev/sda foo
# mount /dev/sda bar
User access mountpoint "foo" | Remount mountpoint "bar"
|
ext4_map_blocks() | ext4_remount()
check_block_validity() | ext4_setup_system_zone()
ext4_data_block_valid() | ext4_release_system_zone()
| free system_blks rb nodes
access system_blks rb nodes |
trigger use after free |
This problem can also be reproduced by one mountpint, At the same time,
add_system_zone() can get called during remount as well so there can be
racing ext4_data_block_valid() reading the rbtree at the same time.
This patch add RCU to protect system zone from releasing or building
when doing a remount which inverse current "noblock_validity" mount
option. It assign the rbtree after the whole tree was complete and
do actual freeing after rcu grace period, avoid any intermediate state.
Signed-off-by: zhangyi (F) <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
---
Changes since v4:
- Update comments before ext4_[setup|release]_system_zone().
- Add reviewed-by tag.
fs/ext4/block_validity.c | 188 ++++++++++++++++++++++++++++++++++-------------
fs/ext4/ext4.h | 10 ++-
2 files changed, 146 insertions(+), 52 deletions(-)
diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c
index 8e83741..003dc1d 100644
--- a/fs/ext4/block_validity.c
+++ b/fs/ext4/block_validity.c
@@ -38,6 +38,7 @@ int __init ext4_init_system_zone(void)
void ext4_exit_system_zone(void)
{
+ rcu_barrier();
kmem_cache_destroy(ext4_system_zone_cachep);
}
@@ -49,17 +50,26 @@ static inline int can_merge(struct ext4_system_zone *entry1,
return 0;
}
+static void release_system_zone(struct ext4_system_blocks *system_blks)
+{
+ struct ext4_system_zone *entry, *n;
+
+ rbtree_postorder_for_each_entry_safe(entry, n,
+ &system_blks->root, node)
+ kmem_cache_free(ext4_system_zone_cachep, entry);
+}
+
/*
* Mark a range of blocks as belonging to the "system zone" --- that
* is, filesystem metadata blocks which should never be used by
* inodes.
*/
-static int add_system_zone(struct ext4_sb_info *sbi,
+static int add_system_zone(struct ext4_system_blocks *system_blks,
ext4_fsblk_t start_blk,
unsigned int count)
{
struct ext4_system_zone *new_entry = NULL, *entry;
- struct rb_node **n = &sbi->system_blks.rb_node, *node;
+ struct rb_node **n = &system_blks->root.rb_node, *node;
struct rb_node *parent = NULL, *new_node = NULL;
while (*n) {
@@ -91,7 +101,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
new_node = &new_entry->node;
rb_link_node(new_node, parent, n);
- rb_insert_color(new_node, &sbi->system_blks);
+ rb_insert_color(new_node, &system_blks->root);
}
/* Can we merge to the left? */
@@ -101,7 +111,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
if (can_merge(entry, new_entry)) {
new_entry->start_blk = entry->start_blk;
new_entry->count += entry->count;
- rb_erase(node, &sbi->system_blks);
+ rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
@@ -112,7 +122,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
entry = rb_entry(node, struct ext4_system_zone, node);
if (can_merge(new_entry, entry)) {
new_entry->count += entry->count;
- rb_erase(node, &sbi->system_blks);
+ rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
@@ -126,7 +136,7 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
int first = 1;
printk(KERN_INFO "System zones: ");
- node = rb_first(&sbi->system_blks);
+ node = rb_first(&sbi->system_blks->root);
while (node) {
entry = rb_entry(node, struct ext4_system_zone, node);
printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ",
@@ -137,7 +147,47 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
printk(KERN_CONT "\n");
}
-static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
+/*
+ * Returns 1 if the passed-in block region (start_blk,
+ * start_blk+count) is valid; 0 if some part of the block region
+ * overlaps with filesystem metadata blocks.
+ */
+static int ext4_data_block_valid_rcu(struct ext4_sb_info *sbi,
+ struct ext4_system_blocks *system_blks,
+ ext4_fsblk_t start_blk,
+ unsigned int count)
+{
+ struct ext4_system_zone *entry;
+ struct rb_node *n;
+
+ if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
+ (start_blk + count < start_blk) ||
+ (start_blk + count > ext4_blocks_count(sbi->s_es))) {
+ sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
+ return 0;
+ }
+
+ if (system_blks == NULL)
+ return 1;
+
+ n = system_blks->root.rb_node;
+ while (n) {
+ entry = rb_entry(n, struct ext4_system_zone, node);
+ if (start_blk + count - 1 < entry->start_blk)
+ n = n->rb_left;
+ else if (start_blk >= (entry->start_blk + entry->count))
+ n = n->rb_right;
+ else {
+ sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
+ return 0;
+ }
+ }
+ return 1;
+}
+
+static int ext4_protect_reserved_inode(struct super_block *sb,
+ struct ext4_system_blocks *system_blks,
+ u32 ino)
{
struct inode *inode;
struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -163,14 +213,15 @@ static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
if (n == 0) {
i++;
} else {
- if (!ext4_data_block_valid(sbi, map.m_pblk, n)) {
+ if (!ext4_data_block_valid_rcu(sbi, system_blks,
+ map.m_pblk, n)) {
ext4_error(sb, "blocks %llu-%llu from inode %u "
"overlap system zone", map.m_pblk,
map.m_pblk + map.m_len - 1, ino);
err = -EFSCORRUPTED;
break;
}
- err = add_system_zone(sbi, map.m_pblk, n);
+ err = add_system_zone(system_blks, map.m_pblk, n);
if (err < 0)
break;
i += n;
@@ -180,94 +231,129 @@ static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
return err;
}
+static void ext4_destroy_system_zone(struct rcu_head *rcu)
+{
+ struct ext4_system_blocks *system_blks;
+
+ system_blks = container_of(rcu, struct ext4_system_blocks, rcu);
+ release_system_zone(system_blks);
+ kfree(system_blks);
+}
+
+/*
+ * Build system zone rbtree which is used for block validity checking.
+ *
+ * The update of system_blks pointer in this function is protected by
+ * sb->s_umount semaphore. However we have to be careful as we can be
+ * racing with ext4_data_block_valid() calls reading system_blks rbtree
+ * protected only by RCU. That's why we first build the rbtree and then
+ * swap it in place.
+ */
int ext4_setup_system_zone(struct super_block *sb)
{
ext4_group_t ngroups = ext4_get_groups_count(sb);
struct ext4_sb_info *sbi = EXT4_SB(sb);
+ struct ext4_system_blocks *system_blks;
struct ext4_group_desc *gdp;
ext4_group_t i;
int flex_size = ext4_flex_bg_size(sbi);
int ret;
if (!test_opt(sb, BLOCK_VALIDITY)) {
- if (sbi->system_blks.rb_node)
+ if (sbi->system_blks)
ext4_release_system_zone(sb);
return 0;
}
- if (sbi->system_blks.rb_node)
+ if (sbi->system_blks)
return 0;
+ system_blks = kzalloc(sizeof(*system_blks), GFP_KERNEL);
+ if (!system_blks)
+ return -ENOMEM;
+
for (i=0; i < ngroups; i++) {
cond_resched();
if (ext4_bg_has_super(sb, i) &&
((i < 5) || ((i % flex_size) == 0)))
- add_system_zone(sbi, ext4_group_first_block_no(sb, i),
+ add_system_zone(system_blks,
+ ext4_group_first_block_no(sb, i),
ext4_bg_num_gdb(sb, i) + 1);
gdp = ext4_get_group_desc(sb, i, NULL);
- ret = add_system_zone(sbi, ext4_block_bitmap(sb, gdp), 1);
+ ret = add_system_zone(system_blks,
+ ext4_block_bitmap(sb, gdp), 1);
if (ret)
- return ret;
- ret = add_system_zone(sbi, ext4_inode_bitmap(sb, gdp), 1);
+ goto err;
+ ret = add_system_zone(system_blks,
+ ext4_inode_bitmap(sb, gdp), 1);
if (ret)
- return ret;
- ret = add_system_zone(sbi, ext4_inode_table(sb, gdp),
+ goto err;
+ ret = add_system_zone(system_blks,
+ ext4_inode_table(sb, gdp),
sbi->s_itb_per_group);
if (ret)
- return ret;
+ goto err;
}
if (ext4_has_feature_journal(sb) && sbi->s_es->s_journal_inum) {
- ret = ext4_protect_reserved_inode(sb,
+ ret = ext4_protect_reserved_inode(sb, system_blks,
le32_to_cpu(sbi->s_es->s_journal_inum));
if (ret)
- return ret;
+ goto err;
}
+ /*
+ * System blks rbtree complete, announce it once to prevent racing
+ * with ext4_data_block_valid() accessing the rbtree at the same
+ * time.
+ */
+ rcu_assign_pointer(sbi->system_blks, system_blks);
+
if (test_opt(sb, DEBUG))
debug_print_tree(sbi);
return 0;
+err:
+ release_system_zone(system_blks);
+ kfree(system_blks);
+ return ret;
}
-/* Called when the filesystem is unmounted */
+/*
+ * Called when the filesystem is unmounted or when remounting it with
+ * noblock_validity specified.
+ *
+ * The update of system_blks pointer in this function is protected by
+ * sb->s_umount semaphore. However we have to be careful as we can be
+ * racing with ext4_data_block_valid() calls reading system_blks rbtree
+ * protected only by RCU. So we first clear the system_blks pointer and
+ * then free the rbtree only after RCU grace period expires.
+ */
void ext4_release_system_zone(struct super_block *sb)
{
- struct ext4_system_zone *entry, *n;
+ struct ext4_system_blocks *system_blks;
- rbtree_postorder_for_each_entry_safe(entry, n,
- &EXT4_SB(sb)->system_blks, node)
- kmem_cache_free(ext4_system_zone_cachep, entry);
+ system_blks = rcu_dereference(EXT4_SB(sb)->system_blks);
+ rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);
- EXT4_SB(sb)->system_blks = RB_ROOT;
+ if (system_blks)
+ call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
}
-/*
- * Returns 1 if the passed-in block region (start_blk,
- * start_blk+count) is valid; 0 if some part of the block region
- * overlaps with filesystem metadata blocks.
- */
int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,
unsigned int count)
{
- struct ext4_system_zone *entry;
- struct rb_node *n = sbi->system_blks.rb_node;
+ struct ext4_system_blocks *system_blks;
+ int ret;
- if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
- (start_blk + count < start_blk) ||
- (start_blk + count > ext4_blocks_count(sbi->s_es))) {
- sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
- return 0;
- }
- while (n) {
- entry = rb_entry(n, struct ext4_system_zone, node);
- if (start_blk + count - 1 < entry->start_blk)
- n = n->rb_left;
- else if (start_blk >= (entry->start_blk + entry->count))
- n = n->rb_right;
- else {
- sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
- return 0;
- }
- }
- return 1;
+ /*
+ * Lock the system zone to prevent it being released concurrently
+ * when doing a remount which inverse current "[no]block_validity"
+ * mount option.
+ */
+ rcu_read_lock();
+ system_blks = rcu_dereference(sbi->system_blks);
+ ret = ext4_data_block_valid_rcu(sbi, system_blks, start_blk,
+ count);
+ rcu_read_unlock();
+ return ret;
}
int ext4_check_blockref(const char *function, unsigned int line,
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index bf660aa..c025efc 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -185,6 +185,14 @@ struct ext4_map_blocks {
};
/*
+ * Block validity checking, system zone rbtree.
+ */
+struct ext4_system_blocks {
+ struct rb_root root;
+ struct rcu_head rcu;
+};
+
+/*
* Flags for ext4_io_end->flags
*/
#define EXT4_IO_END_UNWRITTEN 0x0001
@@ -1421,7 +1429,7 @@ struct ext4_sb_info {
int s_jquota_fmt; /* Format of quota to use */
#endif
unsigned int s_want_extra_isize; /* New inodes should reserve # bytes */
- struct rb_root system_blks;
+ struct ext4_system_blocks __rcu *system_blks;
#ifdef EXTENTS_STATS
/* ext4 extents stats */
--
2.7.4
On Thu, Aug 15, 2019 at 07:47:19PM +0800, zhangyi (F) wrote:
> Remount process will release system zone which was allocated before if
> "noblock_validity" is specified. If we mount an ext4 file system to two
> mountpoints with default mount options, and then remount one of them
> with "noblock_validity", it may trigger a use after free problem when
> someone accessing the other one.
>
> # mount /dev/sda foo
> # mount /dev/sda bar
>
> User access mountpoint "foo" | Remount mountpoint "bar"
> |
> ext4_map_blocks() | ext4_remount()
> check_block_validity() | ext4_setup_system_zone()
> ext4_data_block_valid() | ext4_release_system_zone()
> | free system_blks rb nodes
> access system_blks rb nodes |
> trigger use after free |
>
> This problem can also be reproduced by one mountpint, At the same time,
> add_system_zone() can get called during remount as well so there can be
> racing ext4_data_block_valid() reading the rbtree at the same time.
>
> This patch add RCU to protect system zone from releasing or building
> when doing a remount which inverse current "noblock_validity" mount
> option. It assign the rbtree after the whole tree was complete and
> do actual freeing after rcu grace period, avoid any intermediate state.
>
> Signed-off-by: zhangyi (F) <[email protected]>
> Reviewed-by: Jan Kara <[email protected]>
Applied, thanks!
I changed the patch summary to:
ext4: fix potential use after free after remounting with noblock_validity
I also added:
Reported-by: [email protected]
since this had been noted by Syzkaller:
https://syzkaller.appspot.com/bug?extid=1e470567330b7ad711d5
Cheers,
- Ted
On Sat, Aug 24, 2019 at 11:40:00PM -0400, Theodore Y. Ts'o wrote:
> On Thu, Aug 15, 2019 at 07:47:19PM +0800, zhangyi (F) wrote:
> > Remount process will release system zone which was allocated before if
> > "noblock_validity" is specified. If we mount an ext4 file system to two
> > mountpoints with default mount options, and then remount one of them
> > with "noblock_validity", it may trigger a use after free problem when
> > someone accessing the other one.
> >
> > # mount /dev/sda foo
> > # mount /dev/sda bar
> >
> > User access mountpoint "foo" | Remount mountpoint "bar"
> > |
> > ext4_map_blocks() | ext4_remount()
> > check_block_validity() | ext4_setup_system_zone()
> > ext4_data_block_valid() | ext4_release_system_zone()
> > | free system_blks rb nodes
> > access system_blks rb nodes |
> > trigger use after free |
> >
> > This problem can also be reproduced by one mountpint, At the same time,
> > add_system_zone() can get called during remount as well so there can be
> > racing ext4_data_block_valid() reading the rbtree at the same time.
> >
> > This patch add RCU to protect system zone from releasing or building
> > when doing a remount which inverse current "noblock_validity" mount
> > option. It assign the rbtree after the whole tree was complete and
> > do actual freeing after rcu grace period, avoid any intermediate state.
> >
> > Signed-off-by: zhangyi (F) <[email protected]>
> > Reviewed-by: Jan Kara <[email protected]>
>
> Applied, thanks!
>
> I changed the patch summary to:
>
> ext4: fix potential use after free after remounting with noblock_validity
>
> I also added:
>
> Reported-by: [email protected]
>
> since this had been noted by Syzkaller:
>
> https://syzkaller.appspot.com/bug?extid=1e470567330b7ad711d5
>
> Cheers,
>
> - Ted
This patch is causing:
=============================
WARNING: suspicious RCU usage
5.3.0-rc4-00016-gc747f2a0aa5e #9 Not tainted
-----------------------------
fs/ext4/block_validity.c:333 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by umount/605:
#0: 00000000961e5b1d (&type->s_umount_key#26){++++}, at: deactivate_super+0x130/0x150 fs/super.c:361
stack backtrace:
CPU: 1 PID: 605 Comm: umount Not tainted 5.3.0-rc4-00016-gc747f2a0aa5e #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x86/0xca lib/dump_stack.c:113
lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5357
ext4_release_system_zone+0xfe/0x130 fs/ext4/block_validity.c:333
ext4_put_super+0x18c/0xbb0 fs/ext4/super.c:992
generic_shutdown_super+0x128/0x320 fs/super.c:458
kill_block_super+0x97/0xe0 fs/super.c:1310
deactivate_locked_super+0x7b/0xd0 fs/super.c:331
deactivate_super+0x138/0x150 fs/super.c:362
cleanup_mnt+0x298/0x3f0 fs/namespace.c:1102
__cleanup_mnt+0xd/0x10 fs/namespace.c:1109
task_work_run+0x103/0x180 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x10b/0x130 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
do_syscall_64+0x343/0x450 arch/x86/entry/common.c:299
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7face39bfd77
Code: 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 8
RSP: 002b:00007ffd297f2fb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 000055f7506ae060 RCX: 00007face39bfd77
RDX: 0000000000000001 RSI: 0000000000000000 RDI: 000055f7506b0c90
RBP: 000055f7506b0c90 R08: 000055f7506afec0 R09: 0000000000000014
R10: 00000000000006b4 R11: 0000000000000246 R12: 00007face3ec1e64
R13: 0000000000000000 R14: 000055f7506ae240 R15: 00007ffd297f3240
==================================================================
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
On 2019/8/26 10:56, Theodore Y. Ts'o Wrote:
> 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,
>
Hi Ted，
Sorry about missing this warning, I think switch to use:
system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks);
or
system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true);
is enough to fix this waring, am I missing something?
Thanks,
Yi.
On Mon 26-08-19 16:31:41, zhangyi (F) wrote:
> On 2019/8/26 10:56, Theodore Y. Ts'o Wrote:
> > 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,
> >
>
> Hi Ted，
> Sorry about missing this warning, I think switch to use:
> system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks);
> or
> system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true);
> is enough to fix this waring, am I missing something?
Proper fix for this is actually using:
system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
lockdep_is_held(&sb->s_umount));
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
On 2019/8/26 23:03, Jan Kara Wrote:
> On Mon 26-08-19 16:31:41, zhangyi (F) wrote:
>> On 2019/8/26 10:56, Theodore Y. Ts'o Wrote:
>>> 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,
>>>
>>
>> Hi Ted，
>> Sorry about missing this warning, I think switch to use:
>> system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks);
>> or
>> system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true);
>> is enough to fix this waring, am I missing something?
>
> Proper fix for this is actually using:
>
> system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
> lockdep_is_held(&sb->s_umount));
>
Totally agree, will resend the patch.
Thanks,
Yi.