Re: [PATCH 4/6] f2fs: introduce cp_lock to protect updating of ckpt_flags

From: Jaegeuk Kim
Date: Mon Sep 19 2016 - 22:41:41 EST

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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@xxxxxxxxxx>
> >>
> >> 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.

BTW, we can do multiple set/clear flags in do_checkpoint() with single spin_lock
call, tho.

Thanks,

> >
> >> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> >> ---
> >> 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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