Re: [f2fs-dev] [PATCH v3] f2fs: handle errors of f2fs_get_meta_page_nofail be failed

[Chao Yu]

On 2020/10/13 11:07, jaegeuk@xxxxxxxxxx wrote:
> First problem is we hit BUG_ON() in f2fs_get_sum_page given EIO on
> f2fs_get_meta_page_nofail().
>
> Quick fix was not to give any error with infinite loop, but syzbot caught
> a case where it goes to that loop from fuzzed image. In turned out we abused
> f2fs_get_meta_page_nofail() like in the below call stack.
>
> - f2fs_fill_super
>   - f2fs_build_segment_manager
>    - build_sit_entries
>     - get_current_sit_page
>
> INFO: task syz-executor178:6870 can't die for more than 143 seconds.
> task:syz-executor178 state:R
>   stack:26960 pid: 6870 ppid:  6869 flags:0x00004006
> Call Trace:
>
> Showing all locks held in the system:
> 1 lock held by khungtaskd/1179:
>   #0: ffffffff8a554da0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6242
> 1 lock held by systemd-journal/3920:
> 1 lock held by in:imklog/6769:
>   #0: ffff88809eebc130 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:930
> 1 lock held by syz-executor178/6870:
>   #0: ffff8880925120e0 (&type->s_umount_key#47/1){+.+.}-{3:3}, at: alloc_super+0x201/0xaf0 fs/super.c:229
>
> Actually, we didn't have to use _nofail in this case, since we could return
> error to mount(2) already with the error handler.
>
> As a result, this patch tries to 1) remove _nofail callers as much as possible,
> 2) deal with error case in last remaining caller, f2fs_get_sum_page().
>
> Reported-by: syzbot+ee250ac8137be41d7b13@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

I prefer to use f2fs_get_meta_page() as much as possible except change_curseg()
path, however, it's minor, and the time is closing to merge window, so:

Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>

Thanks,

> ---
>
> Change log from v2:
>   - avoid _nofail and add error handler
>
>   fs/f2fs/checkpoint.c |  2 +-
>   fs/f2fs/f2fs.h       |  2 +-
>   fs/f2fs/node.c       |  2 +-
>   fs/f2fs/segment.c    | 12 +++++++++---
>   4 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> index f18386d30f031..023462e80e58d 100644
> --- a/fs/f2fs/checkpoint.c
> +++ b/fs/f2fs/checkpoint.c
> @@ -107,7 +107,7 @@ struct page *f2fs_get_meta_page(struct f2fs_sb_info *sbi, pgoff_t index)
>   	return __get_meta_page(sbi, index, true);
>   }
>   
> -struct page *f2fs_get_meta_page_nofail(struct f2fs_sb_info *sbi, pgoff_t index)
> +struct page *f2fs_get_meta_page_retry(struct f2fs_sb_info *sbi, pgoff_t index)
>   {
>   	struct page *page;
>   	int count = 0;
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index ae46d44bd5211..adda53d20a399 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3422,7 +3422,7 @@ unsigned int f2fs_usable_blks_in_seg(struct f2fs_sb_info *sbi,
>   void f2fs_stop_checkpoint(struct f2fs_sb_info *sbi, bool end_io);
>   struct page *f2fs_grab_meta_page(struct f2fs_sb_info *sbi, pgoff_t index);
>   struct page *f2fs_get_meta_page(struct f2fs_sb_info *sbi, pgoff_t index);
> -struct page *f2fs_get_meta_page_nofail(struct f2fs_sb_info *sbi, pgoff_t index);
> +struct page *f2fs_get_meta_page_retry(struct f2fs_sb_info *sbi, pgoff_t index);
>   struct page *f2fs_get_tmp_page(struct f2fs_sb_info *sbi, pgoff_t index);
>   bool f2fs_is_valid_blkaddr(struct f2fs_sb_info *sbi,
>   					block_t blkaddr, int type);
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 93fb34d636eb5..d5d8ce077f295 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -109,7 +109,7 @@ static void clear_node_page_dirty(struct page *page)
>   
>   static struct page *get_current_nat_page(struct f2fs_sb_info *sbi, nid_t nid)
>   {
> -	return f2fs_get_meta_page_nofail(sbi, current_nat_addr(sbi, nid));
> +	return f2fs_get_meta_page(sbi, current_nat_addr(sbi, nid));
>   }
>   
>   static struct page *get_next_nat_page(struct f2fs_sb_info *sbi, nid_t nid)
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 13ecd2c2c361b..05ab5ae2b5f7f 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2379,7 +2379,9 @@ int f2fs_npages_for_summary_flush(struct f2fs_sb_info *sbi, bool for_ra)
>    */
>   struct page *f2fs_get_sum_page(struct f2fs_sb_info *sbi, unsigned int segno)
>   {
> -	return f2fs_get_meta_page_nofail(sbi, GET_SUM_BLOCK(sbi, segno));
> +	if (unlikely(f2fs_cp_error(sbi)))
> +		return ERR_PTR(-EIO);
> +	return f2fs_get_meta_page_retry(sbi, GET_SUM_BLOCK(sbi, segno));
>   }
>   
>   void f2fs_update_meta_page(struct f2fs_sb_info *sbi,
> @@ -2669,7 +2671,11 @@ static void change_curseg(struct f2fs_sb_info *sbi, int type, bool flush)
>   	__next_free_blkoff(sbi, curseg, 0);
>   
>   	sum_page = f2fs_get_sum_page(sbi, new_segno);
> -	f2fs_bug_on(sbi, IS_ERR(sum_page));
> +	if (IS_ERR(sum_page)) {
> +		/* GC won't be able to use stale summary pages by cp_error */
> +		memset(curseg->sum_blk, 0, SUM_ENTRY_SIZE);
> +		return;
> +	}
>   	sum_node = (struct f2fs_summary_block *)page_address(sum_page);
>   	memcpy(curseg->sum_blk, sum_node, SUM_ENTRY_SIZE);
>   	f2fs_put_page(sum_page, 1);
> @@ -3964,7 +3970,7 @@ int f2fs_lookup_journal_in_cursum(struct f2fs_journal *journal, int type,
>   static struct page *get_current_sit_page(struct f2fs_sb_info *sbi,
>   					unsigned int segno)
>   {
> -	return f2fs_get_meta_page_nofail(sbi, current_sit_addr(sbi, segno));
> +	return f2fs_get_meta_page(sbi, current_sit_addr(sbi, segno));
>   }
>   
>   static struct page *get_next_sit_page(struct f2fs_sb_info *sbi,