[ 093/104] ext4: fix journal callback list traversal

Greg Kroah-Hartman
2013-05-06T23:18:26Z

From: Dmitry Monakhov <dmonakhov@openvz.org>

commit 5d3ee20855e28169d711b394857ee608a5023094 upstream.

It is incorrect to use list_for_each_entry_safe() for journal callback
traversial because ->next may be removed by other task:
->ext4_mb_free_metadata()
->ext4_mb_free_metadata()
->ext4_journal_callback_del()

This results in the following issue:

WARNING: at lib/list_debug.c:62 __list_del_entry+0x1c0/0x250()
Hardware name:
list_del corruption. prev->next should be ffff88019a4ec198, but was 6b6b6b6b6b6b6b6b
Modules linked in: cpufreq_ondemand acpi_cpufreq freq_table mperf coretemp kvm_intel kvm crc32c_intel ghash_clmulni_intel microcode sg xhci_hcd button sd_mod crc_t10dif aesni_intel ablk_helper cryptd lrw aes_x86_64 xts gf128mul ahci libahci pata_acpi ata_generic dm_mirror dm_region_hash dm_log dm_mod
Pid: 16400, comm: jbd2/dm-1-8 Tainted: G W 3.8.0-rc3+ #107
Call Trace:
[<ffffffff8106fb0d>] warn_slowpath_common+0xad/0xf0
[<ffffffff8106fc06>] warn_slowpath_fmt+0x46/0x50
[<ffffffff813637e9>] ? ext4_journal_commit_callback+0x99/0xc0
[<ffffffff8148cae0>] __list_del_entry+0x1c0/0x250
[<ffffffff813637bf>] ext4_journal_commit_callback+0x6f/0xc0
[<ffffffff813ca336>] jbd2_journal_commit_transaction+0x23a6/0x2570
[<ffffffff8108aa42>] ? try_to_del_timer_sync+0x82/0xa0
[<ffffffff8108b491>] ? del_timer_sync+0x91/0x1e0
[<ffffffff813d3ecf>] kjournald2+0x19f/0x6a0
[<ffffffff810ad630>] ? wake_up_bit+0x40/0x40
[<ffffffff813d3d30>] ? bit_spin_lock+0x80/0x80
[<ffffffff810ac6be>] kthread+0x10e/0x120
[<ffffffff810ac5b0>] ? __init_kthread_worker+0x70/0x70
[<ffffffff818ff6ac>] ret_from_fork+0x7c/0xb0
[<ffffffff810ac5b0>] ? __init_kthread_worker+0x70/0x70

This patch fix the issue as follows:
- ext4_journal_commit_callback() make list truly traversial safe
simply by always starting from list_head
- fix race between two ext4_journal_callback_del() and
ext4_journal_callback_try_del()

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/ext4_jbd2.h | 6 +++++-
fs/ext4/mballoc.c | 8 ++++----
fs/ext4/super.c | 7 +++++--
3 files changed, 14 insertions(+), 7 deletions(-)

--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -170,16 +170,20 @@ static inline void ext4_journal_callback
* ext4_journal_callback_del: delete a registered callback
* @handle: active journal transaction handle on which callback was registered
* @jce: registered journal callback entry to unregister
+ * Return true if object was sucessfully removed
*/
-static inline void ext4_journal_callback_del(handle_t *handle,
+static inline bool ext4_journal_callback_try_del(handle_t *handle,
struct ext4_journal_cb_entry *jce)
{
+ bool deleted;
struct ext4_sb_info *sbi =
EXT4_SB(handle->h_transaction->t_journal->j_private);

spin_lock(&sbi->s_md_lock);
+ deleted = !list_empty(&jce->jce_list);
list_del_init(&jce->jce_list);
spin_unlock(&sbi->s_md_lock);
+ return deleted;
}

int
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4449,11 +4449,11 @@ ext4_mb_free_metadata(handle_t *handle,
node = rb_prev(new_node);
if (node) {
entry = rb_entry(node, struct ext4_free_data, efd_node);
- if (can_merge(entry, new_entry)) {
+ if (can_merge(entry, new_entry) &&
+ ext4_journal_callback_try_del(handle, &entry->efd_jce)) {
new_entry->efd_start_cluster = entry->efd_start_cluster;
new_entry->efd_count += entry->efd_count;
rb_erase(node, &(db->bb_free_root));
- ext4_journal_callback_del(handle, &entry->efd_jce);
kmem_cache_free(ext4_free_data_cachep, entry);
}
}
@@ -4461,10 +4461,10 @@ ext4_mb_free_metadata(handle_t *handle,
node = rb_next(new_node);
if (node) {
entry = rb_entry(node, struct ext4_free_data, efd_node);
- if (can_merge(new_entry, entry)) {
+ if (can_merge(new_entry, entry) &&
+ ext4_journal_callback_try_del(handle, &entry->efd_jce)) {
new_entry->efd_count += entry->efd_count;
rb_erase(node, &(db->bb_free_root));
- ext4_journal_callback_del(handle, &entry->efd_jce);
kmem_cache_free(ext4_free_data_cachep, entry);
}
}
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -452,10 +452,13 @@ static void ext4_journal_commit_callback
struct super_block *sb = journal->j_private;
struct ext4_sb_info *sbi = EXT4_SB(sb);
int error = is_journal_aborted(journal);
- struct ext4_journal_cb_entry *jce, *tmp;
+ struct ext4_journal_cb_entry *jce;

+ BUG_ON(txn->t_state == T_FINISHED);
spin_lock(&sbi->s_md_lock);
- list_for_each_entry_safe(jce, tmp, &txn->t_private_list, jce_list) {
+ while (!list_empty(&txn->t_private_list)) {
+ jce = list_entry(txn->t_private_list.next,
+ struct ext4_journal_cb_entry, jce_list);
list_del_init(&jce->jce_list);
spin_unlock(&sbi->s_md_lock);
jce->jce_func(sb, jce, error);