linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: remove race condition in releasing cblocks

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Message-ID: <CACOAw_z0BU3t7V+BN7TvaO96GckwNh2SRLreGxO60EDbMb_epw@mail.gmail.com>
Date:   Fri, 8 May 2020 15:58:44 +0900
From:   Daeho Jeong <daeho43@...il.com>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: remove race condition in releasing cblocks

I moved checking i_compr_blocks phrase after calling inode_lock()
already, because we should check this after writing pages.

So, if it fails to check i_compr_blocks, we need to call inode_unlock().

Am I missing something?

2020년 5월 8일 (금) 오후 3:50, Chao Yu <yuchao0@...wei.com>님이 작성:
>
> On 2020/5/8 12:25, Daeho Jeong wrote:
> > From: Daeho Jeong <daehojeong@...gle.com>
> >
> > Now, if writing pages and releasing compress blocks occur
> > simultaneously, and releasing cblocks is executed more than one time
> > to a file, then total block count of filesystem and block count of the
> > file could be incorrect and damaged.
> >
> > We have to execute releasing compress blocks only one time for a file
> > without being interfered by writepages path.
> >
> > Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
> > ---
> >  fs/f2fs/file.c | 31 ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> >
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 4aab4b42d8ba..a92bc51b9b28 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -3488,6 +3488,7 @@ static int f2fs_release_compress_blocks(struct file *filp, unsigned long arg)
> >       pgoff_t page_idx = 0, last_idx;
> >       unsigned int released_blocks = 0;
> >       int ret;
> > +     int writecount;
> >
> >       if (!f2fs_sb_has_compression(F2FS_I_SB(inode)))
> >               return -EOPNOTSUPP;
>
> Before inode_lock(), there is one case we may jump to out label, in
> this case, we may unlock inode incorrectly.
>
>         if (!F2FS_I(inode)->i_compr_blocks)
>                 goto out;
>
> > -
> > -     inode_unlock(inode);
> >  out:
> > +     inode_unlock(inode);
> > +
> >       mnt_drop_write_file(filp);
>
> Thanks,