Re: [PATCH] ext4: fix journal callback list traversal

[Dmitry Monakhov <dmonakhov@openvz.org>]

On Thu, 21 Mar 2013 19:49:12 +0400, Dmitry Monakhov <dmonakhov@openvz.org> wrote:
> 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 result in 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 like follows:
> - ext4_journal_commit_callback() make list truly traversial safe
>   simply by always starting from the list head
> - fix race between ext4_journal_callback_del() and
>   ext4_journal_callback_try_del()
OOps. Sorry. I've sent wrong patch. Please ignore it. I'll send correct
version in a minute.

> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
> ---
>  fs/ext4/ext4_jbd2.h |    6 +++++-
>  fs/ext4/mballoc.c   |    8 ++++----
>  fs/ext4/super.c     |    4 +++-
>  3 files changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
> index 4c216b1..aeed0ba 100644
> --- a/fs/ext4/ext4_jbd2.h
> +++ b/fs/ext4/ext4_jbd2.h
> @@ -194,16 +194,20 @@ static inline void ext4_journal_callback_add(handle_t *handle,
>   * 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
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index ee6614b..2815f46 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4420,11 +4420,11 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
>  	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);
>  		}
>  	}
> @@ -4432,10 +4432,10 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
>  	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_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);
>  		}
>  	}
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index d1ee6a8..c7e1509 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -352,7 +352,9 @@ static void ext4_journal_commit_callback(journal_t *journal, transaction_t *txn)
>  	struct ext4_journal_cb_entry	*jce, *tmp;
>  
>  	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);
> -- 
> 1.7.1
> 
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