Re: [f2fs-dev] [PATCH] f2fs: reset free segment to prefree status when do_checkpoint() fail

[Chao Yu]

On 2021/4/27 16:21, Yangtao Li wrote:
> When do_checkpoint() fails, the prefree bitmap is not cleared,
> but these segments are already in the free state. If these segments
> are used, the segments in use will be reset to the free state when
> f2fs_clear_prefree_segments is called next time.
>
> So reset free segments to prefree status when do_checkpoint() fail
> to avoid this situation.
>
> Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
> ---
>   fs/f2fs/checkpoint.c |  6 ++++--
>   fs/f2fs/f2fs.h       |  1 +
>   fs/f2fs/segment.c    | 13 +++++++++++++
>   fs/f2fs/segment.h    |  7 ++++++-
>   4 files changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index be5415a0dbbc..0200af4d02ef 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -1647,10 +1647,12 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>   	f2fs_save_inmem_curseg(sbi);
>   
>   	err = do_checkpoint(sbi, cpc);
> -	if (err)
> +	if (err) {
>   		f2fs_release_discard_addrs(sbi);
> -	else
> +		f2fs_set_free_as_prefree_segments(sbi);
> +	} else {
>   		f2fs_clear_prefree_segments(sbi, cpc);
> +	}
>   
>   	f2fs_restore_inmem_curseg(sbi);
>   stop:
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index e2d302ae3a46..1618e9a74e89 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3369,6 +3369,7 @@ bool f2fs_is_checkpointed_data(struct f2fs_sb_info *sbi, block_t blkaddr);
>   void f2fs_drop_discard_cmd(struct f2fs_sb_info *sbi);
>   void f2fs_stop_discard_thread(struct f2fs_sb_info *sbi);
>   bool f2fs_issue_discard_timeout(struct f2fs_sb_info *sbi);
> +void f2fs_set_free_as_prefree_segments(struct f2fs_sb_info *sbi);
>   void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
>   					struct cp_control *cpc);
>   void f2fs_dirty_to_prefree(struct f2fs_sb_info *sbi);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index c2866561263e..334e499a0f43 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1959,6 +1959,19 @@ static void set_prefree_as_free_segments(struct f2fs_sb_info *sbi)
>   	mutex_unlock(&dirty_i->seglist_lock);
>   }
>   
> +void f2fs_set_free_as_prefree_segments(struct f2fs_sb_info *sbi)
> +{
> +	struct dirty_seglist_info *dirty_i = DIRTY_I(sbi);
> +	unsigned int segno;
> +
> +	mutex_lock(&dirty_i->seglist_lock);
> +	for_each_set_bit(segno, dirty_i->dirty_segmap[PRE], MAIN_SEGS(sbi)) {
> +		if (__set_test_and_inuse(sbi, segno))
> +			test_and_clear_bit(segno, dirty_i->dirty_segmap[PRE]);
> +	}
> +	mutex_unlock(&dirty_i->seglist_lock);
> +}
> +
>   void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
>   						struct cp_control *cpc)
>   {
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index e9a7a637d688..5da8d1100b87 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -487,19 +487,24 @@ static inline void __set_test_and_free(struct f2fs_sb_info *sbi,
>   	spin_unlock(&free_i->segmap_lock);
>   }
>   
> -static inline void __set_test_and_inuse(struct f2fs_sb_info *sbi,
> +static inline bool __set_test_and_inuse(struct f2fs_sb_info *sbi,
>   		unsigned int segno)
>   {
>   	struct free_segmap_info *free_i = FREE_I(sbi);
>   	unsigned int secno = GET_SEC_FROM_SEG(sbi, segno);
> +	bool is_inuse = false;
>   
>   	spin_lock(&free_i->segmap_lock);
>   	if (!test_and_set_bit(segno, free_i->free_segmap)) {
>   		free_i->free_segments--;
>   		if (!test_and_set_bit(secno, free_i->free_secmap))

if (!IS_CURSEC(sbi, secno) &&
	!test_and_set_bit(secno, free_i->free_secmap))

I think just reverting dirty/free bitmap is not enough if checkpoint fails,
due to we have updated sbi->cur_cp_pack and nat/sit bitmap, next CP tries
to overwrite last valid meta/node/data, then filesystem will be corrupted.

So I suggest to set cp_error if do_checkpoint() fails until we can handle
all cases, which is not so easy.

How do you think?

Thanks,

>   			free_i->free_sections--;
> +	} else {
> +		is_inuse = true;
>   	}
>   	spin_unlock(&free_i->segmap_lock);
> +
> +	return is_inuse;
>   }
>   
>   static inline void get_sit_bitmap(struct f2fs_sb_info *sbi,