Re: [PATCH] f2fs: submit cached data bios before gc_merge GC

[Chao Yu <chao@kernel.org>]

I've submitted the same fix previously as below:

https://lore.kernel.org/linux-f2fs-devel/20260519011438.1168155-1-chao@kernel.org

On 5/21/26 13:30, Wenjie Qi wrote:
> Commit fefdf0723650 ("f2fs: fix potential deadlock in f2fs_balance_fs()")
> added cached DATA bio submission before direct foreground GC in
> f2fs_balance_fs().
> 
> This avoids a deadlock between writeback and GC on cached data folios.
> However, when gc_merge is enabled, f2fs_balance_fs() does not execute
> foreground GC in the caller. It wakes the background GC thread and waits
> for that foreground request to finish.
> 
> That branch currently skips the cached DATA bio submission, so the same
> foreground GC request can still start with cached DATA bios pending.
> 
> Move the cached DATA bio submission before the gc_merge branch so both
> direct and merged foreground GC paths satisfy the same precondition.
> 
> Fixes: fefdf0723650 ("f2fs: fix potential deadlock in f2fs_balance_fs()")
> Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
> ---
>   fs/f2fs/segment.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 7c8ac62b1b0..1ef4edb7707 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -445,6 +445,13 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>   	if (has_enough_free_secs(sbi, 0, 0))
>   		return;
>   
> +	/*
> +	 * Submit all cached OPU/IPU DATA bios before triggering
> +	 * foreground GC to avoid potential deadlocks.
> +	 */
> +	f2fs_submit_merged_write(sbi, DATA);
> +	f2fs_submit_all_merged_ipu_writes(sbi);
> +
>   	if (test_opt(sbi, GC_MERGE) && sbi->gc_thread &&
>   				sbi->gc_thread->f2fs_gc_task) {
>   		DEFINE_WAIT(wait);
> @@ -464,13 +471,6 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>   			.err_gc_skipped = false,
>   			.nr_free_secs = 1 };
>   
> -		/*
> -		 * Submit all cached OPU/IPU DATA bios before triggering
> -		 * foreground GC to avoid potential deadlocks.
> -		 */
> -		f2fs_submit_merged_write(sbi, DATA);
> -		f2fs_submit_all_merged_ipu_writes(sbi);
> -
>   		f2fs_down_write_trace(&sbi->gc_lock, &gc_control.lc);
>   		stat_inc_gc_call_count(sbi, FOREGROUND);
>   		f2fs_gc(sbi, &gc_control);