Re: [f2fs-dev] [PATCH v2] f2fs: fix to freeze GC and discard threads quickly

[Chao Yu <chao@kernel.org>]

On 3/12/2026 11:53 PM, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> Suspend can fail if kernel threads do not freeze for a while.
> f2fs_gc and f2fs_discard threads can perform long-running operations
> that prevent them from reaching a freeze point in a timely manner.
> 
> This patch adds explicit freezing checks in the following locations:
> 1. f2fs_gc: Added a check at the 'retry' label to exit the loop quickly
>     if freezing is requested, especially during heavy GC rounds.
> 2. __issue_discard_cmd: Added a 'suspended' flag to break both inner and
>     outer loops during discard command issuance if freezing is detected
>     after at least one command has been issued.
> 3. __issue_discard_cmd_orderly: Added a similar check for orderly discard
>     to ensure responsiveness.
> 
> These checks ensure that the threads release locks safely and enter the
> frozen state.
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
> v2: add freezing check in do_garbage_collect()
> ---
>   fs/f2fs/gc.c      | 10 ++++++++++
>   fs/f2fs/segment.c | 14 ++++++++++++--
>   2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 981eac629fe9..f07746a14aa4 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -1883,12 +1883,18 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>   				sbi->next_victim_seg[gc_type] =
>   					(cur_segno + 1 < sec_end_segno) ?
>   					cur_segno + 1 : NULL_SEGNO;
> +
> +			if (unlikely(freezing(current))) {
> +				folio_put_refs(sum_folio, 2);
> +				goto stop;
> +			}
>   		}
>   next_block:
>   		folio_put_refs(sum_folio, 2);
>   		segno = block_end_segno;
>   	}
>   
> +stop:
>   	if (submitted)
>   		f2fs_submit_merged_write(sbi, data_type);
>   
> @@ -1962,6 +1968,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>   		goto stop;
>   	}
>   retry:
> +	if (unlikely(freezing(current))) {
> +		ret = 0;
> +		goto stop;
> +	}
>   	ret = __get_victim(sbi, &segno, gc_type, gc_control->one_time);
>   	if (ret) {
>   		/* allow to search victim from sections has pinned data */
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index e9b6d774b985..a6c82ab28288 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1606,6 +1606,9 @@ static void __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>   		if (dc->state != D_PREP)
>   			goto next;
>   
> +		if (*issued > 0 && unlikely(freezing(current)))
> +			break;
> +
>   		if (dpolicy->io_aware && !is_idle(sbi, DISCARD_TIME)) {
>   			io_interrupted = true;
>   			break;
> @@ -1645,6 +1648,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>   	struct blk_plug plug;
>   	int i, issued;
>   	bool io_interrupted = false;
> +	bool suspended = false;
>   
>   	if (dpolicy->timeout)
>   		f2fs_update_time(sbi, UMOUNT_DISCARD_TIMEOUT);
> @@ -1675,6 +1679,11 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>   		list_for_each_entry_safe(dc, tmp, pend_list, list) {
>   			f2fs_bug_on(sbi, dc->state != D_PREP);
>   
> +			if (issued > 0 && unlikely(freezing(current))) {
> +				suspended = true;
> +				break;
> +			}
> +
>   			if (dpolicy->timeout &&
>   				f2fs_time_over(sbi, UMOUNT_DISCARD_TIMEOUT))
>   				break;
> @@ -1694,11 +1703,12 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>   next:
>   		mutex_unlock(&dcc->cmd_lock);
>   
> -		if (issued >= dpolicy->max_requests || io_interrupted)
> +		if (issued >= dpolicy->max_requests || io_interrupted ||
> +					suspended)
>   			break;
>   	}
>   
> -	if (dpolicy->type == DPOLICY_UMOUNT && issued) {
> +	if (dpolicy->type == DPOLICY_UMOUNT && issued && !suspended) {

We don't need to change this line due to we don't care about suspend
during umount()? Right?

Thanks,

>   		__wait_all_discard_cmd(sbi, dpolicy);
>   		goto retry;
>   	}