Subject: Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount root fs

From: Sabrina Dubroca <[email-masked]>
Date: Tue, 20 Jan 2015 21:45:04 +0100

2015-01-20, 19:54:32 +0000, Al Viro wrote:
> On Tue, Jan 20, 2015 at 06:51:35PM +0100, Sabrina Dubroca wrote:
> > 2015-01-20, 12:39:08 -0500, Paul Moore wrote:
> > > On Tuesday, January 20, 2015 05:56:55 PM Sabrina Dubroca wrote:
> > > > Hello,
> > > > 
> > > > Today's linux-next doesn't boot on my qemu VM:
> > > 
> > > ...
> > >  
> > > > I bisected it down to:
> > > > 
> > > > 5dc5218840e1  fs: create proper filename objects using getname_kernel()
> > > > 
> > > > I reverted then reapplied each part of that patch.  It works if I
> > > > leave out the hunk for do_path_lookup:
> > > > 
> > > > diff --git a/fs/namei.c b/fs/namei.c
> > > > index eeb3b83661f8..c3d21b79090e 100644
> > > > --- a/fs/namei.c
> > > > +++ b/fs/namei.c
> > > > @@ -2001,9 +2001,15 @@ static int filename_lookup(int dfd, struct filename
> > > > *name, static int do_path_lookup(int dfd, const char *name,
> > > >  				unsigned int flags, struct nameidata *nd)
> > > >  {
> > > > -	struct filename filename = { .name = name };
> > > > +	int retval;
> > > > +	struct filename *filename;
> > > > 
> > > > -	return filename_lookup(dfd, &filename, flags, nd);
> > > > +	filename = getname_kernel(name);
> > > > +	if (unlikely(IS_ERR(filename)))
> > > > +		return PTR_ERR(filename);
> > > > +	retval = filename_lookup(dfd, filename, flags, nd);
> > > > +	putname(filename);
> > > > +	return retval;
> > > >  }
> > > > 
> > > > I don't know what other info you may need.
> > > > Full dmesg for the failed boot included below.
> > > 
> > > Thanks for testing this and reporting the problem, especially such a small 
> > > bisection.  Unfortunately nothing is immediately obvious to me, would you mind 
> > > sharing your kernel config so I can try to reproduce and debug the problem?
> > 
> > Sure.
> > 
> > I run qemu with:
> > 
> > qemu-system-x86_64 -enable-kvm -cpu host  -m 512 -kernel bzImage -append 'root=/dev/sda1' $IMG
> > 
> > and the image contains a single ext4 partition with a basic ArchLinux install.
> 
> Could you turn that return PTR_ERR(filename); into 
> {
> 	printk(KERN_ERR "failed(%p -> %d)", name, PTR_ERR(filename));
> 	return PTR_ERR(filename);
> }
> reproduce the panic and see what has it produced?

Nothing.

Not sure if it helps, but I added after filename_lookup:

printk(KERN_ERR "fn_lookup %s %d\n", name, retval);

and I get:

[    1.618558] fn_lookup bsg/0:0:0:0 -2
[    1.619437] fn_lookup bsg 0
[    1.620236] fn_lookup bsg/0:0:0:0 -2
[    1.625996] fn_lookup sda 0
[    1.626609] fn_lookup sda 0
[    1.639007] fn_lookup sda1 0
[    1.639691] fn_lookup sda1 0
[    1.643656] fn_lookup bsg/1:0:0:0 -2
[    1.644974] fn_lookup bsg 0
[    1.645928] fn_lookup bsg/1:0:0:0 -2
[    1.649483] fn_lookup /dev/ram -2
[    1.650424] fn_lookup /dev/root -2
[    1.651234] VFS: Cannot open root device "sda1" or unknown-block(8,1): error -2

-- 
Sabrina