linux-kernel - Re: [PATCH] ubifs: Add freeze support

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Date:   Tue, 30 May 2017 11:37:40 +0900
From:   Hyunchul Lee <hyc.lee@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     Artem Bityutskiy <dedekind1@...il.com>, adrian.hunter@...el.com,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        linux-mtd@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] ubifs: Add freeze support

On Mon, May 29, 2017 at 10:42:37AM +0200, Richard Weinberger wrote:
> Hyunchul,
> 
> Am 29.05.2017 um 04:24 schrieb Hyunchul Lee:
> >>> This is just broken.  First ubifs should still properly propagate
> >>> the errors, and second freezing/unfreezing read only file systems is
> >>> perfectly valid, 
> >>
> >> it is right.
> > 
> > if updating TNC is failed, ubifs might become inconsistant and be switched to 
> > read-only mode. for example, when ubifs_jnl_update is called to create a file, 
> > if inserting a znode for new inode is failed, TNC has only a znode for 
> > new dentry. and this can be only recoverd by replay.
> > 
> > is it required to fix this?
> 
> UBIFS is designed to be power-cut tolerant.
> So, UBIFS must not corrupt in any case.
> 
> Which failure are you facing?
> 
> I have the feeling that you try to paper over some other issue. :-)

The failure hasn't happened. I wondered the following situation
should be handled.

ubifs_create
  ubifs_jnl_update
    write_head
    ubifs_tnc_add_nm  /* (1) add dentry to TNC */
    ubifs_tnc_add     /* (2) add new inode to TNC */
    ubifs_tnc_add     /* (3) add parent inode to TNC */

If ubifs_tnc_add(2) fails, TNC would have the index of a dentry 
which points to an invalid inode. So, though ubifs_readdir
emits the dentry, this inode cannot be accessed. Becasue
there isn't the index of the inode.

I know this situation is hardly probable. But UBIFS would
be read-only and inconsitant in this situation, until replay
is completed.

> 
> Thanks,
> //richard

-- 

Thanks,
Hyunchul