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Date: Tue, 20 Sep 2016 10:50:49 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>
CC: Chao Yu <chao@...nel.org>,
<linux-f2fs-devel@...ts.sourceforge.net>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] f2fs: introduce cp_lock to protect updating of
ckpt_flags
On 2016/9/20 10:41, Jaegeuk Kim wrote:
> On Tue, Sep 20, 2016 at 09:47:20AM +0800, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2016/9/20 5:49, Jaegeuk Kim wrote:
>>> Hi Chao,
>>>
>>> On Sun, Sep 18, 2016 at 11:30:06PM +0800, Chao Yu wrote:
>>>> From: Chao Yu <yuchao0@...wei.com>
>>>>
>>>> This patch introduces spinlock to protect updating process of ckpt_flags
>>>> field in struct f2fs_checkpoint, it avoids incorrectly updating in race
>>>> condition.
>>>
>>> So, I'm seeing a race condition between f2fs_stop_checkpoint(),
>>> write_checkpoint(), and f2fs_fill_super().
>>>
>>> How about just adding f2fs_lock_op() in f2fs_stop_checkpoint()?
>>
>> I'm afraid there will be a potential deadlock here:
>>
>> Thread A Thread B
>> - write_checkpoint
>> - block_operations
>> - f2fs_lock_all
>> - do_checkpoint
>> - wait_on_all_pages_writeback
>> - f2fs_write_end_io
>> - f2fs_stop_checkpoint
>> - f2fs_lock_op
>> - end_page_writeback
>> - atomic_dec_and_test
>> - wake_up
>>
>> Right?
>
> Okay, I see. Let me try to understand in more details.
> Basically, there'd be no problem if there is no f2fs_stop_checkpoint(), since
> every {set|clear}_ckpt_flags() are called under f2fs_lock_op() or in
> fill_super(). And, you're probably concerned about any breakage of ckpt->flags
> due to accidental f2fs_stop_checkpoint() trigger. So, we're able to lose
> ERROR_FLAG because of data race.
>
> Oh, I found one potential corruption case in f2fs_write_checkpoint().
> Before writing the last checkpoint block, we used to check its IO error.
> But, if set_ckpt_flags() and f2fs_stop_checkpoint() were called concurrently,
> ckpt_flags was able to lose ERROR_FLAG, resulting in finalizing its checkpoint
> pack. So, we can get valid checkpoint pack with EIO'ed metadata block.
That's right.
>
> BTW, we can do multiple set/clear flags in do_checkpoint() with single spin_lock
> call, tho.
Agree, let me refactor the code. :)
Thanks,
>
> Thanks,
>
>>>
>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>> ---
>>>> fs/f2fs/checkpoint.c | 24 ++++++++++++------------
>>>> fs/f2fs/f2fs.h | 29 +++++++++++++++++++++--------
>>>> fs/f2fs/recovery.c | 2 +-
>>>> fs/f2fs/segment.c | 4 ++--
>>>> fs/f2fs/super.c | 5 +++--
>>>> 5 files changed, 39 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>> index df56a43..0338f8c 100644
>>>> --- a/fs/f2fs/checkpoint.c
>>>> +++ b/fs/f2fs/checkpoint.c
>>>> @@ -28,7 +28,7 @@ struct kmem_cache *inode_entry_slab;
>>>>
>>>> void f2fs_stop_checkpoint(struct f2fs_sb_info *sbi, bool end_io)
>>>> {
>>>> - set_ckpt_flags(sbi->ckpt, CP_ERROR_FLAG);
>>>> + set_ckpt_flags(sbi, CP_ERROR_FLAG);
>>>> sbi->sb->s_flags |= MS_RDONLY;
>>>> if (!end_io)
>>>> f2fs_flush_merged_bios(sbi);
>>>> @@ -571,7 +571,7 @@ int recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>> block_t start_blk, orphan_blocks, i, j;
>>>> int err;
>>>>
>>>> - if (!is_set_ckpt_flags(F2FS_CKPT(sbi), CP_ORPHAN_PRESENT_FLAG))
>>>> + if (!is_set_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG))
>>>> return 0;
>>>>
>>>> start_blk = __start_cp_addr(sbi) + 1 + __cp_payload(sbi);
>>>> @@ -595,7 +595,7 @@ int recover_orphan_inodes(struct f2fs_sb_info *sbi)
>>>> f2fs_put_page(page, 1);
>>>> }
>>>> /* clear Orphan Flag */
>>>> - clear_ckpt_flags(F2FS_CKPT(sbi), CP_ORPHAN_PRESENT_FLAG);
>>>> + clear_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
>>>> return 0;
>>>> }
>>>>
>>>> @@ -1054,9 +1054,9 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>>> /* 2 cp + n data seg summary + orphan inode blocks */
>>>> data_sum_blocks = npages_for_summary_flush(sbi, false);
>>>> if (data_sum_blocks < NR_CURSEG_DATA_TYPE)
>>>> - set_ckpt_flags(ckpt, CP_COMPACT_SUM_FLAG);
>>>> + set_ckpt_flags(sbi, CP_COMPACT_SUM_FLAG);
>>>> else
>>>> - clear_ckpt_flags(ckpt, CP_COMPACT_SUM_FLAG);
>>>> + clear_ckpt_flags(sbi, CP_COMPACT_SUM_FLAG);
>>>>
>>>> orphan_blocks = GET_ORPHAN_BLOCKS(orphan_num);
>>>> ckpt->cp_pack_start_sum = cpu_to_le32(1 + cp_payload_blks +
>>>> @@ -1072,22 +1072,22 @@ static int do_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>>> orphan_blocks);
>>>>
>>>> if (cpc->reason == CP_UMOUNT)
>>>> - set_ckpt_flags(ckpt, CP_UMOUNT_FLAG);
>>>> + set_ckpt_flags(sbi, CP_UMOUNT_FLAG);
>>>> else
>>>> - clear_ckpt_flags(ckpt, CP_UMOUNT_FLAG);
>>>> + clear_ckpt_flags(sbi, CP_UMOUNT_FLAG);
>>>>
>>>> if (cpc->reason == CP_FASTBOOT)
>>>> - set_ckpt_flags(ckpt, CP_FASTBOOT_FLAG);
>>>> + set_ckpt_flags(sbi, CP_FASTBOOT_FLAG);
>>>> else
>>>> - clear_ckpt_flags(ckpt, CP_FASTBOOT_FLAG);
>>>> + clear_ckpt_flags(sbi, CP_FASTBOOT_FLAG);
>>>>
>>>> if (orphan_num)
>>>> - set_ckpt_flags(ckpt, CP_ORPHAN_PRESENT_FLAG);
>>>> + set_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
>>>> else
>>>> - clear_ckpt_flags(ckpt, CP_ORPHAN_PRESENT_FLAG);
>>>> + clear_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
>>>>
>>>> if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
>>>> - set_ckpt_flags(ckpt, CP_FSCK_FLAG);
>>>> + set_ckpt_flags(sbi, CP_FSCK_FLAG);
>>>>
>>>> /* update SIT/NAT bitmap */
>>>> get_sit_bitmap(sbi, __bitmap_ptr(sbi, SIT_BITMAP));
>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>> index c30f744b..b615f3f 100644
>>>> --- a/fs/f2fs/f2fs.h
>>>> +++ b/fs/f2fs/f2fs.h
>>>> @@ -814,6 +814,7 @@ struct f2fs_sb_info {
>>>>
>>>> /* for checkpoint */
>>>> struct f2fs_checkpoint *ckpt; /* raw checkpoint pointer */
>>>> + spinlock_t cp_lock; /* for flag in ckpt */
>>>> struct inode *meta_inode; /* cache meta blocks */
>>>> struct mutex cp_mutex; /* checkpoint procedure lock */
>>>> struct rw_semaphore cp_rwsem; /* blocking FS operations */
>>>> @@ -1083,24 +1084,36 @@ static inline unsigned long long cur_cp_version(struct f2fs_checkpoint *cp)
>>>> return le64_to_cpu(cp->checkpoint_ver);
>>>> }
>>>>
>>>> -static inline bool is_set_ckpt_flags(struct f2fs_checkpoint *cp, unsigned int f)
>>>> +static inline bool is_set_ckpt_flags(struct f2fs_sb_info *sbi, unsigned int f)
>>>> {
>>>> + struct f2fs_checkpoint *cp = F2FS_CKPT(sbi);
>>>> unsigned int ckpt_flags = le32_to_cpu(cp->ckpt_flags);
>>>> +
>>>> return ckpt_flags & f;
>>>> }
>>>>
>>>> -static inline void set_ckpt_flags(struct f2fs_checkpoint *cp, unsigned int f)
>>>> +static inline void set_ckpt_flags(struct f2fs_sb_info *sbi, unsigned int f)
>>>> {
>>>> - unsigned int ckpt_flags = le32_to_cpu(cp->ckpt_flags);
>>>> + struct f2fs_checkpoint *cp = F2FS_CKPT(sbi);
>>>> + unsigned int ckpt_flags;
>>>> +
>>>> + spin_lock(&sbi->cp_lock);
>>>> + ckpt_flags = le32_to_cpu(cp->ckpt_flags);
>>>> ckpt_flags |= f;
>>>> cp->ckpt_flags = cpu_to_le32(ckpt_flags);
>>>> + spin_unlock(&sbi->cp_lock);
>>>> }
>>>>
>>>> -static inline void clear_ckpt_flags(struct f2fs_checkpoint *cp, unsigned int f)
>>>> +static inline void clear_ckpt_flags(struct f2fs_sb_info *sbi, unsigned int f)
>>>> {
>>>> - unsigned int ckpt_flags = le32_to_cpu(cp->ckpt_flags);
>>>> + struct f2fs_checkpoint *cp = F2FS_CKPT(sbi);
>>>> + unsigned int ckpt_flags;
>>>> +
>>>> + spin_lock(&sbi->cp_lock);
>>>> + ckpt_flags = le32_to_cpu(cp->ckpt_flags);
>>>> ckpt_flags &= (~f);
>>>> cp->ckpt_flags = cpu_to_le32(ckpt_flags);
>>>> + spin_unlock(&sbi->cp_lock);
>>>> }
>>>>
>>>> static inline bool f2fs_discard_en(struct f2fs_sb_info *sbi)
>>>> @@ -1148,8 +1161,8 @@ static inline bool __remain_node_summaries(int reason)
>>>>
>>>> static inline bool __exist_node_summaries(struct f2fs_sb_info *sbi)
>>>> {
>>>> - return (is_set_ckpt_flags(F2FS_CKPT(sbi), CP_UMOUNT_FLAG) ||
>>>> - is_set_ckpt_flags(F2FS_CKPT(sbi), CP_FASTBOOT_FLAG));
>>>> + return (is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG) ||
>>>> + is_set_ckpt_flags(sbi, CP_FASTBOOT_FLAG));
>>>> }
>>>>
>>>> /*
>>>> @@ -1851,7 +1864,7 @@ static inline int f2fs_readonly(struct super_block *sb)
>>>>
>>>> static inline bool f2fs_cp_error(struct f2fs_sb_info *sbi)
>>>> {
>>>> - return is_set_ckpt_flags(sbi->ckpt, CP_ERROR_FLAG);
>>>> + return is_set_ckpt_flags(sbi, CP_ERROR_FLAG);
>>>> }
>>>>
>>>> static inline bool is_dot_dotdot(const struct qstr *str)
>>>> diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
>>>> index ad748e5..37d99d2 100644
>>>> --- a/fs/f2fs/recovery.c
>>>> +++ b/fs/f2fs/recovery.c
>>>> @@ -649,7 +649,7 @@ out:
>>>> invalidate_mapping_pages(META_MAPPING(sbi),
>>>> blkaddr, blkaddr);
>>>>
>>>> - set_ckpt_flags(sbi->ckpt, CP_ERROR_FLAG);
>>>> + set_ckpt_flags(sbi, CP_ERROR_FLAG);
>>>> mutex_unlock(&sbi->cp_mutex);
>>>> } else if (need_writecp) {
>>>> struct cp_control cpc = {
>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>> index 101b58f..dc68f30 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -1825,7 +1825,7 @@ static int restore_curseg_summaries(struct f2fs_sb_info *sbi)
>>>> int type = CURSEG_HOT_DATA;
>>>> int err;
>>>>
>>>> - if (is_set_ckpt_flags(F2FS_CKPT(sbi), CP_COMPACT_SUM_FLAG)) {
>>>> + if (is_set_ckpt_flags(sbi, CP_COMPACT_SUM_FLAG)) {
>>>> int npages = npages_for_summary_flush(sbi, true);
>>>>
>>>> if (npages >= 2)
>>>> @@ -1922,7 +1922,7 @@ static void write_normal_summaries(struct f2fs_sb_info *sbi,
>>>>
>>>> void write_data_summaries(struct f2fs_sb_info *sbi, block_t start_blk)
>>>> {
>>>> - if (is_set_ckpt_flags(F2FS_CKPT(sbi), CP_COMPACT_SUM_FLAG))
>>>> + if (is_set_ckpt_flags(sbi, CP_COMPACT_SUM_FLAG))
>>>> write_compacted_summaries(sbi, start_blk);
>>>> else
>>>> write_normal_summaries(sbi, start_blk, CURSEG_HOT_DATA);
>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>> index 555217f..f809729 100644
>>>> --- a/fs/f2fs/super.c
>>>> +++ b/fs/f2fs/super.c
>>>> @@ -735,7 +735,7 @@ static void f2fs_put_super(struct super_block *sb)
>>>> * clean checkpoint again.
>>>> */
>>>> if (is_sbi_flag_set(sbi, SBI_IS_DIRTY) ||
>>>> - !is_set_ckpt_flags(F2FS_CKPT(sbi), CP_UMOUNT_FLAG)) {
>>>> + !is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>>>> struct cp_control cpc = {
>>>> .reason = CP_UMOUNT,
>>>> };
>>>> @@ -1477,6 +1477,7 @@ static void init_sb_info(struct f2fs_sb_info *sbi)
>>>> mutex_init(&sbi->umount_mutex);
>>>> mutex_init(&sbi->wio_mutex[NODE]);
>>>> mutex_init(&sbi->wio_mutex[DATA]);
>>>> + spin_lock_init(&sbi->cp_lock);
>>>>
>>>> #ifdef CONFIG_F2FS_FS_ENCRYPTION
>>>> memcpy(sbi->key_prefix, F2FS_KEY_DESC_PREFIX,
>>>> @@ -1818,7 +1819,7 @@ try_onemore:
>>>> * previous checkpoint was not done by clean system shutdown.
>>>> */
>>>> if (bdev_read_only(sb->s_bdev) &&
>>>> - !is_set_ckpt_flags(sbi->ckpt, CP_UMOUNT_FLAG)) {
>>>> + !is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>>>> err = -EROFS;
>>>> goto free_kobj;
>>>> }
>>>> --
>>>> 2.7.2
>>>
>>> .
>>>
>
> .
>
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