Re: [PATCH] ext4: properly check for dirty state in ext4_inode_datasync_dirty()

[Ritesh Harjani]

On 10/27/20 3:58 AM, harshad shirwadkar wrote:
> Thanks Andrea for catching and sending out a fix for this.
>
> On Sat, Oct 24, 2020 at 7:01 AM Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote:
> > ext4_inode_datasync_dirty() needs to return 'true' if the inode is
> > dirty, 'false' otherwise, but the logic seems to be incorrectly changed
> > by commit aa75f4d3daae ("ext4: main fast-commit commit path").
> >
> > This introduces a problem with swap files that are always failing to be
> > activated, showing this error in dmesg:
> >
> >   [   34.406479] swapon: file is not committed

Well, I too noticed this yesterday while I was testing xfstests -g swap.
Those tests were returning _notrun, hence that could be the reason why
it didn't get notice in XFSTESTing from Ted.

- I did notice that this code was introduced in v10 only.
This wasn't there in v9 though.


> > Simple test case to reproduce the problem:
> >
> >    # fallocate -l 8G swapfile
> >    # chmod 0600 swapfile
> >    # mkswap swapfile
> >    # swapon swapfile
> >
> > Fix the logic to return the proper state of the inode.
> >
> > Link: https://lore.kernel.org/lkml/20201024131333.GA32124@xps-13-7390
> > Fixes: aa75f4d3daae ("ext4: main fast-commit commit path")
> > Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
> > ---
> >   fs/ext4/inode.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 03c2253005f0..a890a17ab7e1 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -3308,8 +3308,8 @@ static bool ext4_inode_datasync_dirty(struct inode *inode)
> >          if (journal) {
> >                  if (jbd2_transaction_committed(journal,
> >                                          EXT4_I(inode)->i_datasync_tid))
> > -                       return true;
> > -               return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) >=
> > +                       return false;
> > +               return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
> >                          EXT4_I(inode)->i_fc_committed_subtid;
> In addition, the above condition should only be checked if fast
> commits are enabled. So, in effect this overall condition will look
> like this:
>
> if (journal) {
>      if (jbd2_transaction_committed(journal, EXT4_I(inode)->i_datasync_tid))
>          return false;
>      if (test_opt2(sb, JOURNAL_FAST_COMMIT))
>          return atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid) <
> EXT4_I(inode)->i_fc_committed_subtid;
>      return true;
> }

Yup - I too had made a similar patch. But then I also noticed that below
condition will always remain false. Since we never update
"i_fc_committed_subtid" other than at these 2 places
(one during init where we set it to 0 and other during ext4_fc_commit()
where we set it to sbi->s_fc_subtid).

<condition>
atomic_read(&EXT4_SB(inode->i_sb)->s_fc_subtid < 
EXT4_I(inode)->i_fc_committed_subtid


Maybe I need more reading around this.

-ritesh





> Thanks,
> Harshad
>
> >          }
> >
> > --
> > 2.27.0