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Date:   Fri, 21 Jun 2019 11:02:06 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Chao Yu <yuchao0@huawei.com>, Qiuyang Sun <sunqiuyang@huawei.com>,
        linux-f2fs-devel@lists.sourceforge.net,
        Linux-Next <linux-next@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH -next] f2fs: Use div_u64*() for 64-bit divisions
Message-ID: <20190621180206.GD79502@jaegeuk-macbookpro.roam.corp.google.com>
References: <20190620143800.20640-1-geert@linux-m68k.org>
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 <CAMuHMdUHi3z5xmLyut2XqOPf9XFMF3AJiTnkwOAL-GQ6Ck_1ow@mail.gmail.com>
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On 06/21, Geert Uytterhoeven wrote:
> Hi Chao,
> 
> On Fri, Jun 21, 2019 at 11:54 AM Chao Yu <yuchao0@huawei.com> wrote:
> > Since the original patch hasn't been merged to upstream, I think we can merge
> > this into original patch, how do you think?
> 
> Thanks, that's fine for me.

Merged the fix.
Thank you so much.

> 
> > On 2019/6/20 22:38, Geert Uytterhoeven wrote:
> > > On 32-bit (e.g. m68k):
> > >
> > >     fs/f2fs/gc.o: In function `f2fs_resize_fs':
> > >     gc.c:(.text+0x3056): undefined reference to `__umoddi3'
> > >     gc.c:(.text+0x30c4): undefined reference to `__udivdi3'
> > >
> > > Fix this by using div_u64_rem() and div_u64() for 64-by-32 modulo resp.
> > > division operations.
> > >
> > > Reported-by: noreply@ellerman.id.au
> > > Fixes: d2ae7494d043bfaf ("f2fs: ioctl for removing a range from F2FS")
> > > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > > ---
> > > This assumes BLKS_PER_SEC(sbi) is 32-bit.
> > >
> > >     #define BLKS_PER_SEC(sbi)                                       \
> > >           ((sbi)->segs_per_sec * (sbi)->blocks_per_seg)
> > >
> > > Notes:
> > >   1. f2fs_sb_info.segs_per_sec and f2fs_sb_info.blocks_per_seg are both
> > >      unsigned int,
> > >   2. The multiplication is done in 32-bit arithmetic, hence the result
> > >      is of type unsigned int.
> > >   3. Is it guaranteed that the result will always fit in 32-bit, or can
> > >      this overflow?
> > >   4. fs/f2fs/debug.c:update_sit_info() assigns BLKS_PER_SEC(sbi) to
> > >      unsigned long long blks_per_sec, anticipating a 64-bit value.
> > > ---
> > >  fs/f2fs/gc.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> > > index 5b1076505ade9f84..c65f87f11de029f4 100644
> > > --- a/fs/f2fs/gc.c
> > > +++ b/fs/f2fs/gc.c
> > > @@ -1438,13 +1438,15 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > >       unsigned int secs;
> > >       int gc_mode, gc_type;
> > >       int err = 0;
> > > +     __u32 rem;
> > >
> > >       old_block_count = le64_to_cpu(F2FS_RAW_SUPER(sbi)->block_count);
> > >       if (block_count > old_block_count)
> > >               return -EINVAL;
> > >
> > >       /* new fs size should align to section size */
> > > -     if (block_count % BLKS_PER_SEC(sbi))
> > > +     div_u64_rem(block_count, BLKS_PER_SEC(sbi), &rem);
> > > +     if (rem)
> > >               return -EINVAL;
> > >
> > >       if (block_count == old_block_count)
> > > @@ -1463,7 +1465,7 @@ int f2fs_resize_fs(struct f2fs_sb_info *sbi, __u64 block_count)
> > >       freeze_bdev(sbi->sb->s_bdev);
> > >
> > >       shrunk_blocks = old_block_count - block_count;
> > > -     secs = shrunk_blocks / BLKS_PER_SEC(sbi);
> > > +     secs = div_u64(shrunk_blocks, BLKS_PER_SEC(sbi));
> > >       spin_lock(&sbi->stat_lock);
> > >       if (shrunk_blocks + valid_user_blocks(sbi) +
> > >               sbi->current_reserved_blocks + sbi->unusable_block_count +
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> -- 
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds