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

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Message-ID: <11d60b1c-7c9a-709e-4d51-7e89fabba6a0@nod.at>
Date:   Tue, 30 May 2017 09:51:00 +0200
From:   Richard Weinberger <richard@....at>
To:     Hyunchul Lee <hyc.lee@...il.com>
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

Hyunchul,

Am 30.05.2017 um 04:37 schrieb Hyunchul Lee:
>> 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.

Well, to make ubifs_jnl_update() more robust wrt. such unlikely failures
please rework the journal code.
Adding freeze support does not fix the root cause.
UBIFS treats unrecoverable errors in ubifs_jnl_* since ever as fatal.

Thanks,
//richard