Re: [f2fs-dev] [PATCH v3] f2fs: add a rw_sem to cover quota flag changes

From: Chao Yu
Date: Tue Jun 11 2019 - 03:50:46 EST

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On 2019/6/5 2:36, Jaegeuk Kim wrote:
> Two paths to update quota and f2fs_lock_op:
>
> 1.
> - lock_op
> | - quota_update
> `- unlock_op
>
> 2.
> - quota_update
> - lock_op
> `- unlock_op
>
> But, we need to make a transaction on quota_update + lock_op in #2 case.
> So, this patch introduces:
> 1. lock_op
> 2. down_write
> 3. check __need_flush
> 4. up_write
> 5. if there is dirty quota entries, flush them
> 6. otherwise, good to go
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
>
> v3 from v2:
> - refactor to fix quota corruption issue
> : it seems that the previous scenario is not real and no deadlock case was
> encountered.

- f2fs_dquot_commit
- down_read(&sbi->quota_sem)
- block_operation
- f2fs_lock_all
- need_flush_quota
- down_write(&sbi->quota_sem)
- f2fs_quota_write
- f2fs_lock_op

Why can't this happen?

Once more question, should we hold quota_sem during checkpoint to avoid further
quota update? f2fs_lock_op can do this job as well?

Thanks,

>
> fs/f2fs/checkpoint.c | 41 +++++++++++++++++++----------------------
> fs/f2fs/f2fs.h | 1 +
> fs/f2fs/super.c | 26 +++++++++++++++++++++-----
> 3 files changed, 41 insertions(+), 27 deletions(-)
>
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index 89825261d474..43f65f0962e5 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1131,17 +1131,24 @@ static void __prepare_cp_block(struct f2fs_sb_info *sbi)
>
> static bool __need_flush_quota(struct f2fs_sb_info *sbi)
> {
> + bool ret = false;
> +
> if (!is_journalled_quota(sbi))
> return false;
> - if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH))
> - return false;
> - if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR))
> - return false;
> - if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH))
> - return true;
> - if (get_pages(sbi, F2FS_DIRTY_QDATA))
> - return true;
> - return false;
> +
> + down_write(&sbi->quota_sem);
> + if (is_sbi_flag_set(sbi, SBI_QUOTA_SKIP_FLUSH)) {
> + ret = false;
> + } else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_REPAIR)) {
> + ret = false;
> + } else if (is_sbi_flag_set(sbi, SBI_QUOTA_NEED_FLUSH)) {
> + clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> + ret = true;
> + } else if (get_pages(sbi, F2FS_DIRTY_QDATA)) {
> + ret = true;
> + }
> + up_write(&sbi->quota_sem);
> + return ret;
> }
>
> /*
> @@ -1160,26 +1167,22 @@ static int block_operations(struct f2fs_sb_info *sbi)
> blk_start_plug(&plug);
>
> retry_flush_quotas:
> + f2fs_lock_all(sbi);
> if (__need_flush_quota(sbi)) {
> int locked;
>
> if (++cnt > DEFAULT_RETRY_QUOTA_FLUSH_COUNT) {
> set_sbi_flag(sbi, SBI_QUOTA_SKIP_FLUSH);
> - f2fs_lock_all(sbi);
> + set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> goto retry_flush_dents;
> }
> - clear_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
> + f2fs_unlock_all(sbi);
>
> /* only failed during mount/umount/freeze/quotactl */
> locked = down_read_trylock(&sbi->sb->s_umount);
> f2fs_quota_sync(sbi->sb, -1);
> if (locked)
> up_read(&sbi->sb->s_umount);
> - }
> -
> - f2fs_lock_all(sbi);
> - if (__need_flush_quota(sbi)) {
> - f2fs_unlock_all(sbi);
> cond_resched();
> goto retry_flush_quotas;
> }
> @@ -1201,12 +1204,6 @@ static int block_operations(struct f2fs_sb_info *sbi)
> */
> down_write(&sbi->node_change);
>
> - if (__need_flush_quota(sbi)) {
> - up_write(&sbi->node_change);
> - f2fs_unlock_all(sbi);
> - goto retry_flush_quotas;
> - }
> -
> if (get_pages(sbi, F2FS_DIRTY_IMETA)) {
> up_write(&sbi->node_change);
> f2fs_unlock_all(sbi);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 9674a85154b2..9bd2bf0f559b 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1253,6 +1253,7 @@ struct f2fs_sb_info {
> block_t unusable_block_count; /* # of blocks saved by last cp */
>
> unsigned int nquota_files; /* # of quota sysfile */
> + struct rw_semaphore quota_sem; /* blocking cp for flags */
>
> /* # of pages, see count_type */
> atomic_t nr_pages[NR_COUNT_TYPE];
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 15d7e30bfc72..5a318399a2fa 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1964,6 +1964,7 @@ int f2fs_quota_sync(struct super_block *sb, int type)
> int cnt;
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_writeback_dquots(sb, type);
> if (ret)
> goto out;
> @@ -2001,6 +2002,7 @@ int f2fs_quota_sync(struct super_block *sb, int type)
> out:
> if (ret)
> set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> @@ -2094,32 +2096,40 @@ static void f2fs_truncate_quota_inode_pages(struct super_block *sb)
>
> static int f2fs_dquot_commit(struct dquot *dquot)
> {
> + struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_commit(dquot);
> if (ret < 0)
> - set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> + set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> static int f2fs_dquot_acquire(struct dquot *dquot)
> {
> + struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_acquire(dquot);
> if (ret < 0)
> - set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> -
> + set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> static int f2fs_dquot_release(struct dquot *dquot)
> {
> + struct f2fs_sb_info *sbi = F2FS_SB(dquot->dq_sb);
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_release(dquot);
> if (ret < 0)
> - set_sbi_flag(F2FS_SB(dquot->dq_sb), SBI_QUOTA_NEED_REPAIR);
> + set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> @@ -2129,22 +2139,27 @@ static int f2fs_dquot_mark_dquot_dirty(struct dquot *dquot)
> struct f2fs_sb_info *sbi = F2FS_SB(sb);
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_mark_dquot_dirty(dquot);
>
> /* if we are using journalled quota */
> if (is_journalled_quota(sbi))
> set_sbi_flag(sbi, SBI_QUOTA_NEED_FLUSH);
>
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> static int f2fs_dquot_commit_info(struct super_block *sb, int type)
> {
> + struct f2fs_sb_info *sbi = F2FS_SB(sb);
> int ret;
>
> + down_read(&sbi->quota_sem);
> ret = dquot_commit_info(sb, type);
> if (ret < 0)
> - set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);
> + set_sbi_flag(sbi, SBI_QUOTA_NEED_REPAIR);
> + up_read(&sbi->quota_sem);
> return ret;
> }
>
> @@ -3253,6 +3268,7 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
> }
>
> init_rwsem(&sbi->cp_rwsem);
> + init_rwsem(&sbi->quota_sem);
> init_waitqueue_head(&sbi->cp_wait);
> init_sb_info(sbi);
>
>

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