Re: [PATCH 1/1] ubifs: Try to recover from missing znode

[Zhihao Cheng]

在 2024/10/9 20:49, Benedikt Spranger 写道:
> On Wed, 9 Oct 2024 18:46:43 +0800
> Zhihao Cheng <chengzhihao1@xxxxxxxxxx> wrote:
>
> > 在 2024/10/9 14:03, Richard Weinberger 写道:
> > > ----- Ursprüngliche Mail -----
> > > > Von: "chengzhihao1" <chengzhihao1@xxxxxxxxxx>
> > > > An: "Benedikt Spranger" <b.spranger@xxxxxxxxxxxxx>, "linux-kernel"
> > > > <linux-kernel@xxxxxxxxxxxxxxx> CC: "linux-mtd"
> > > > <linux-mtd@xxxxxxxxxxxxxxxxxxx>, "richard" <richard@xxxxxx>
> > > > Gesendet: Mittwoch, 9. Oktober 2024 04:23:02 Betreff: Re: [PATCH
> > > > 1/1] ubifs: Try to recover from missing znode
> > >
> > > > 在 2024/10/8 21:33, Benedikt Spranger 写道:
> > > > > After powercut on a system using ubifs mounting failed:
> > > > >
> > > > > 2024-09-30T12:38:26.880487+02:00 sonja kernel: UBIFS error
> > > > > (ubi0:0 pid 2178): ubifs_read_node [ubifs]: bad node type (255
> > > > > but expected 9) 2024-09-30T12:38:26.880506+02:00 sonja kernel:
> > > > > UBIFS error (ubi0:0 pid 2178): ubifs_read_node [ubifs]: bad node
> > > > > at LEB 103:46920, LEB mapping status 0
> > > > > 2024-09-30T12:38:26.880509+02:00 sonja kernel: Not a node, first
> > > > > 24 bytes: 2024-09-30T12:38:26.880510+02:00 sonja kernel:
> > > > > 00000000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > > > > ff ff ff ff ff ff ........................
> > > > >
> > > > > While traversing over zbranches during the journal replay one
> > > > > zbranch points to a znode, which was not written to the flash and
> > > > > therefore the flash is empty.
> > > >
> > > > UBIFS guarantees two things for znodes:
> > > > 1) all index nodes(in commit seq N) are written on flash before
> > > > master nodes(for commit seq N) are written.
> > > > 2) all index nodes(in commit seq N) won't be erased from flash
> > > > before master nodes(for commit seq N+1) are written.
> > > > So, I don't understand that why znodes not exist during journal
> > > > replaying?
> > >
> > > In addition to that, is just one znode missing or are larger parts
> > > of the flash empty?
>
> Some background:
> The system producing the broken image runs on an older kernel version
> (4.9.286-rt189). Attaching UBI performs without any error. It seems,
> that there is only one znode missing. There are empty parts on the
> flash, but as far as I can see all PEBs have UBI header Information.
> The missing znode is somewhere in th middle of an PEB and other znodes
> are in that PEB.
>
> > After reviewing the TNC related code, I cannot find out any illegal
> > behaviors to make znode lost or valid index LEB erased.
> OK. Is it possible, that this behaviour is caused by a already fixed
> bug? This happend on a system running 4.9.286-rt189.

I found one patch [1], which fixes a data lost problem while writing failed.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.12-rc2&id=31a149d5c13c4cbcf97de3435817263a2d8c9d6e
> > Hi Benedikt, could you provide a corrupted UBIFS image? Let me try
> > getting more information.
> I need to clarify this.
>
> Regards
>      Benedikt Spranger
> .