linux-kernel - Re: [PATCH 1/2] f2fs: Fix mount failure due to SPO after a successful online resize FS

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Date:   Mon, 2 Mar 2020 10:09:48 +0530
From:   Sahitya Tummala <stummala@...eaurora.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     Jaegeuk Kim <jaegeuk@...nel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, stummala@...eaurora.org
Subject: Re: [PATCH 1/2] f2fs: Fix mount failure due to SPO after a
 successful online resize FS

Hi Chao,

On Fri, Feb 28, 2020 at 04:35:37PM +0800, Chao Yu wrote:
> Hi Sahitya,
> 
> Good catch.
> 
> On 2020/2/27 18:39, Sahitya Tummala wrote:
> > Even though online resize is successfully done, a SPO immediately
> > after resize, still causes below error in the next mount.
> > 
> > [   11.294650] F2FS-fs (sda8): Wrong user_block_count: 2233856
> > [   11.300272] F2FS-fs (sda8): Failed to get valid F2FS checkpoint
> > 
> > This is because after FS metadata is updated in update_fs_metadata()
> > if the SBI_IS_DIRTY is not dirty, then CP will not be done to reflect
> > the new user_block_count.
> > 
> > Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
> > ---
> >  fs/f2fs/gc.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > index a92fa49..a14a75f 100644
> > --- a/fs/f2fs/gc.c
> > +++ b/fs/f2fs/gc.c
> > @@ -1577,6 +1577,7 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> >  
> >  	update_fs_metadata(sbi, -secs);
> >  	clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
> 
> Need a barrier here to keep order in between above code and set_sbi_flag(DIRTY)?

I don't think a barrier will help here. Let us say there is a another context
doing CP already, then it races with update_fs_metadata(), so it may or may not
see the resize updates and it will also clear the SBI_IS_DIRTY flag set by resize
(even with a barrier).

I think we need to synchronize this with CP context, so that these resize changes
will be reflected properly. Please see the new diff below and help with the review.

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a14a75f..5554af8 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1467,6 +1467,7 @@ static void update_fs_metadata(struct f2fs_sb_info *sbi, int secs)
        long long user_block_count =
                                le64_to_cpu(F2FS_CKPT(sbi)->user_block_count);

+       clear_sbi_flag(sbi, SBI_IS_DIRTY);
        SM_I(sbi)->segment_count = (int)SM_I(sbi)->segment_count + segs;
        MAIN_SEGS(sbi) = (int)MAIN_SEGS(sbi) + segs;
        FREE_I(sbi)->free_sections = (int)FREE_I(sbi)->free_sections + secs;
@@ -1575,9 +1576,12 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
                goto out;
        }

+       mutex_lock(&sbi->cp_mutex);
        update_fs_metadata(sbi, -secs);
        clear_sbi_flag(sbi, SBI_IS_RESIZEFS);
        set_sbi_flag(sbi, SBI_IS_DIRTY);
+       mutex_unlock(&sbi->cp_mutex);
+
        err = f2fs_sync_fs(sbi->sb, 1);
        if (err) {
                update_fs_metadata(sbi, secs);

thanks,

> 
> > +	set_sbi_flag(sbi, SBI_IS_DIRTY);
> >  	err = f2fs_sync_fs(sbi->sb, 1);
> >  	if (err) {
> >  		update_fs_metadata(sbi, secs);
> 
> Do we need to add clear_sbi_flag(, SBI_IS_DIRTY) into update_fs_metadata(), so above
> path can be covered as well?
> 
> Thanks,
> 
> > 

-- 
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