[OpenWrt-Devel] Device tree issues with TL-WDR4900 (mpc85xx) and kernel 4.0.1

[Felix Fietkau]

On 2015-05-07 08:01, Wojciech Dubowik wrote:
> Try to boot with kernel locking enabled. I have seen jffs2 deadlocks on 
> readdir. As far as I remember
> with this patch it went through but I don't know anymore whether I have 
> changed sth in config.
> 
> Have a look at (search engine...) [PATCH] fs: jffs2: Add setup code for 
> spi nor flash.
> 
> Even with this patch I got some possible dead lock warnings so it might 
> be just a partial cure. BTW it's
> a bit scary for future use. Looks like jffs2 doesn't get enough care...
I believe the locking issues are an overlayfs regression, maybe even
the same one as this one (which I fixed years ago):
http://linux-fsdevel.vger.kernel.narkive.com/XRtXLDlf/patch-1-2-overlayfs-fix-a-deadlock-in-ovl-dir-read-merged

I believe this is the cause of the regression:

commit 49c21e1cacd74a8c83407c70ad860c994e606e25
Author: Miklos Szeredi <mszeredi at suse.cz>
Date:   Sat Dec 13 00:59:42 2014 +0100

    ovl: check whiteout while reading directory
    
    Don't make a separate pass for checking whiteouts, since we can do it while
    reading the upper directory.
    
    This will make it easier to handle multiple layers.
    
    Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>

It probably happens like this:
overlayfs does a readdir, in which jffs2 takes a lock.