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Date: Tue, 26 Mar 2013 22:48:26 +0100
From: Jan Kara <jack@...e.cz>
To: Dmitry Monakhov <dmonakhov@...nvz.org>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
wenqing.lz@...bao.com
Subject: Re: [PATCH 2/3] ext4: fix journal callback list traversal
On Fri 22-03-13 20:18:42, Dmitry Monakhov 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 list_head
> - fix race between two ext4_journal_callback_del() and
> ext4_journal_callback_try_del()
Nasty! The fix is correct just one style nit below. But feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.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..2e5196a 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);
Ah, the indentation is evil here. It made me think you don't use the
return value of ext4_journal_callback_try_del() for a while. Please indent
it like:
if (can_merge(entry, new_entry) &&
ext4_journal_callback_try_del(handle, > &entry->efd_jce)) {
fooo
Honza
> }
> }
> @@ -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_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);
> }
> }
> 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
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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