Re: ubifs: corrupted dirent (ENOENT), problably related to O_TMPFILE and linkat

[Richard Weinberger <richard@nod.at>]

----- Ursprüngliche Mail -----
> Von: sg@emlix.com
> An: "linux-mtd" <linux-mtd@lists.infradead.org>
> CC: "richard" <richard@nod.at>, "Artem Bityutskiy" <dedekind1@gmail.com>, "Adrian Hunter" <adrian.hunter@intel.com>,
> "chengzhihao1" <chengzhihao1@huawei.com>
> Gesendet: Donnerstag, 22. Juli 2021 09:53:24
> Betreff: ubifs: corrupted dirent (ENOENT), problably related to O_TMPFILE and linkat

> Hi,
> 
> we encountered an error in ubifs most likely when using O_TMPFILE and linkat.
> 
> The code (dir.c:ubifs_lookup) we ran into states
> 
>        /*
>         * This should not happen. Probably the file-system needs
>         * checking.
>         */
> I'd love to, but how? since recovery.c should have taken care of that before
> AFAIK

UBIFS code sometimes contains a little portion of humor.
 
> 
> I wish I could give more elaborate information but this one is hard to track
> and reproduce.
> 
> What has been tried so far and also was the first encounter
> 
> - systemd-coredump has been triggered (in our test-setup with kill -SIGABRT of
>  some process)
> - hardware power-cut (the timing when to poweroff has yet to be found)
> - on replaying the journal the fs was mounted read only
> - on later boots the fs was mounted properly but when accessing the respective
>  directory an inode could not be found (with ls).
>  Traced it down to ubifs_tnc_lookup.
> - dead directory entry error lead to ro_mode
> 
> Following part of dmesg shows the error
> 
>   [   67.480858] UBIFS DBG gen (pid 241): dir ino 93, f_pos 0x0
>   [   67.481634] UBIFS DBG gen (pid 241): ino 40735, new f_pos 0x295e98
>   [   67.482024] UBIFS DBG gen (pid 241): ino 98493, new f_pos 0x9f9a65
>   [   67.482753] UBIFS DBG gen (pid 241): ino 98146, new f_pos 0x18b5dd81
>   [   67.483257] UBIFS DBG gen (pid 241): 'tmp' in dir ino 93
>   [   67.486920] UBIFS DBG gen (pid 241):
>   'core.WPEWebProcess.0.e7c55980c230401d8e3941e72f56a95c.251.1530017543000000' in
>   dir ino 93
>   [   67.489412] UBIFS error (ubi0:2 pid 241): ubifs_iget: failed to read inode
>   98493, error -2
> 
> 
> systemd-coredump opens a file with O_TMPFILE, writes to it and later calls
> linkat()
> With O_TMPFILE disabled in kernel the error does not occur and systemd uses an
> alternate code path.

In this area we had a lot of issues, simply because the concept of inode "rebirth"
was unknown to UBIFS.

> System
> 
>  Linux 4.19.186 #26 SMP Wed Jul 21 13:19:08 CEST 2021 armv7l GNU/Linux

This is new enough to contain ee1438ce5dc4 ("ubifs: Check link count of inodes when killing orphans.").
So it must be something different.

> 
> with following patches of which I thought they might solve the problem
>  325b731983d010d358505bf2c40f5e0069af62d2

You want this one definitely. It could explain the problem you see.
BTW: Applying this patch will not recover the corrupted fs. It just makes sure
that the corruption does not happen. 

>  dd7db149bcd914db8fdeb19cd5597c0740121bc7

This one is unrelated. In worst case you'll hit an UBIFS assert.

> /data/var is bind-mounted to /var the directory used by systemd-coredump.
> /data is the actual mountpoint of ubi volume ubi0_2
> 
>  systemd version 239
> 
> Hardware
>  i.MX6Q on a phyCore SOM with a SPANSION S34ML08G201TFI00 NAND flash
> 
>  The power-cut is done hard by pulling the CPU reset line.
> 
> 
> Can you give me hints how to proceed on this?
> - are there any patches from 5.14-rc2 I might have missed
> - how to reproduce the error more reliable, ie. find the right time to cut power
>  It is now at around 4s after issueing 'kill'. With a margin of 500ms
>  and step width of 25ms

Can you reproduce using a recent kernel?

> - with the mentioned above I might get my hands on more useful
>  information than the blank tnc and journal spam with enabled DEBUG (had to set
>  LOG_BUF to
>  24 (16M) to capture/save all messages
> - how to recover by hand

Without inspecting the filesystem this impossible to answer.
You have some recovery tool in mind?

> - might it be safe to just get rid of the inode in ubifs_readdir when it can not
>  be found? In our particular case it is just a coredump an we don't care for
>  data loss as long as we can still use the rest of the volume/
>  filesystem.

Yes. Maybe it makes sense to make UBIFS at this stage more forgiving instead of
the current situation.

Thanks,
//richard

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