UBIFS: ubifs_recover_leb() always execute fix_unclean_leb() even all the nodes are valid

[Zhihao Cheng]

在 2021/12/24 15:58, 韩仁杰 写道:
Hi, 仁杰
> I've been working on Linux 4.4.60 recently When using UBIFS file system,
> 
> I recently encountered a problem that every time I power off and restart,
> 
> I will enter the recovery process of UBIFS.
> 
> 
> 
> I do understand the reason for entering recovery during startup, and the
> 
> main  purpose of ubifs_recover_leb() is to deal with an invalid node and
> 
> make ubifs mount successfully. But even if there are no invalid nodes,
> 
> ubifs_recover_leb() will call  fix_unclean_leb(), which results in flash’s erase
> 
> and write operations during startup.
> 
> 
> 
> I checked the modify history of kernel/fs/ubifs/recovery.c, and found a related
> 
> commit:
> 
>    http://git.infradead.org/linux.git/commitdiff/7c47bfd0dbb20e5d7fa4e37cfd76bb7
> 
> 3d39b32b4?hp=617992069513c1e789c707c4d75ff03bf7dd0fb0.
> 
> 
> 
> In the commit, variable "need_clean" was deleted. My question is that
> whether it is
> 
> necessary to execute fix_unclean_leb() if there are no invalid node ?
> I am not sure if
> 
> there are some additional considerations I didn't think of ?

According to the description in commit 
7c47bfd0dbb20e5d7fa4e37cfd76bb73d39b32b4("UBIFS: always cleanup the 
recovered LEB"):
"Now when we call 'ubifs_recover_leb()' only for LEBs which are 
potentially corrupted (i.e., only for last buds, not for all of them), 
we can cleanup every LEB, not only those where we find corruption. The 
reason - unstable bits. Even though the LEB may look good now, it might 
contain unstable bits which may hit us a bit later."

I guess imporved ubifs_recover_leb() can handle unstable writing on nand 
flash by calling fix_unclean_leb() after a power-cut. Last programming 
before power-cut on PEB is untrustable, even though the PEB is 
recognized as valid for the moment, there maybe another data content 
read from the same PEB after a while. Just like commit said, unstable 
bits, which may fail ubifs_scan().