RE: [PATCH] init: Add bdev fs printk if mount_block_root failed

[Angus Chen]

> -----Original Message-----
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Sent: Friday, May 19, 2023 4:02 AM
> To: Angus Chen <angus.chen@xxxxxxxxxxxxxxx>
> Cc: masahiroy@xxxxxxxxxx; vbabka@xxxxxxx; peterz@xxxxxxxxxxxxx;
> ndesaulniers@xxxxxxxxxx; paulmck@xxxxxxxxxx; rppt@xxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH] init: Add bdev fs printk if mount_block_root failed
> 
> On Thu, 18 May 2023 11:53:21 +0800 Angus Chen
> <angus.chen@xxxxxxxxxxxxxxx> wrote:
> 
> > Attempt to printk all bdev fstype as root gives the following kernel panic:
> >
> > [    1.729006] VFS: Cannot open root device "vda" or unknown-block(253,0):
> error -19
> > [    1.730603] Please append a correct "root=" boot option; here are the
> available partitions:
> > [    1.732323] fd00          256000 vda
> > [    1.732329]  driver: virtio_blk
> > [    1.734194] Kernel panic - not syncing: VFS: Unable to mount root fs on
> unknown-block(253,0)
> > [    1.734771] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.4.0-rc2+ #53
> > [    1.735194] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
> BIOS 1.10.2-1ubuntu1 04/01/2014
> > [    1.735772] Call Trace:
> > [    1.735950]  <TASK>
> > [    1.736113]  dump_stack_lvl+0x32/0x50
> > [    1.736367]  panic+0x108/0x310
> > [    1.736570]  mount_block_root+0x161/0x310
> > [    1.736849]  ? rdinit_setup+0x40/0x40
> > [    1.737088]  prepare_namespace+0x10c/0x180
> > [    1.737393]  kernel_init_freeable+0x354/0x450
> > [    1.737707]  ? rest_init+0xd0/0xd0
> > [    1.737945]  kernel_init+0x16/0x130
> > [    1.738196]  ret_from_fork+0x1f/0x30
> >
> > QEMU command line:
> > "qemu-system-x86_64 -append root=/dev/vda rootfstype=ext4 ..."
> >
> > This error is because ext4 is not buildin and request ext4 module fail.
> >
> > As a hint, printk all the bdev fstype available for prompts.
> >
> 
> Seems reasonable.  I reworded the changelog a bit:
> 
> : Booting with the QEMU command line:
> : "qemu-system-x86_64 -append root=/dev/vda rootfstype=ext4 ..."
> : will panic if ext4 is not builtin and a request to load the ext4 module
> : fails.
> :
> : [    1.729006] VFS: Cannot open root device "vda" or unknown-block(253,0):
> error -19
> : [    1.730603] Please append a correct "root=" boot option; here are the
> available partitions:
> : [    1.732323] fd00          256000 vda
> : [    1.732329]  driver: virtio_blk
> : [    1.734194] Kernel panic - not syncing: VFS: Unable to mount root fs on
> unknown-block(253,0)
> : [    1.734771] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.4.0-rc2+ #53
> : [    1.735194] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> 1.10.2-1ubuntu1 04/01/2014
> : [    1.735772] Call Trace:
> : [    1.735950]  <TASK>
> : [    1.736113]  dump_stack_lvl+0x32/0x50
> : [    1.736367]  panic+0x108/0x310
> : [    1.736570]  mount_block_root+0x161/0x310
> : [    1.736849]  ? rdinit_setup+0x40/0x40
> : [    1.737088]  prepare_namespace+0x10c/0x180
> : [    1.737393]  kernel_init_freeable+0x354/0x450
> : [    1.737707]  ? rest_init+0xd0/0xd0
> : [    1.737945]  kernel_init+0x16/0x130
> : [    1.738196]  ret_from_fork+0x1f/0x30
> :
> : As a hint, print all the bdev fstypes which are available.
Thank you for your reply. more readable now.
> 
> > --- a/init/do_mounts.c
> > +++ b/init/do_mounts.c
> > @@ -427,8 +427,19 @@ void __init mount_block_root(char *name, int flags)
> >  		printk("VFS: Cannot open root device \"%s\" or %s: error %d\n",
> >  				root_device_name, b, err);
> >  		printk("Please append a correct \"root=\" boot option; here are the
> available partitions:\n");
> > -
> >  		printk_all_partitions();
> > +
> > +		if (root_fs_names)
> > +			num_fs = list_bdev_fs_names(fs_names, PAGE_SIZE);
> > +		if (!num_fs)
> > +			pr_err("Can't find any bdev filesystem to be used for mount!\n");
> > +		else {
> > +			pr_err("List of all bdev filesystem:\n");
> > +			for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1)
> > +				pr_err(" %s", p);
> > +			pr_err("\n");
> > +		}
> > +
> >  		panic("VFS: Unable to mount root fs on %s", b);
> >  	}
> >  	if (!(flags & SB_RDONLY)) {
> 
> And I added a little fix.
> 
> --- a/init/do_mounts.c~init-add-bdev-fs-printk-if-mount_block_root-failed-fix
> +++ a/init/do_mounts.c
> @@ -434,7 +434,7 @@ retry:
>  		if (!num_fs)
>  			pr_err("Can't find any bdev filesystem to be used for mount!\n");
>  		else {
> -			pr_err("List of all bdev filesystem:\n");
> +			pr_err("List of all bdev filesystems:\n");
>  			for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1)
>  				pr_err(" %s", p);
>  			pr_err("\n");
> _
> 
> 
> This function now uses a jumble of printk() and pr_err().  Perhaps
> someone will go through and rationalize all of this sometime.
Yes, I took the printk first but got a warning from checkpatch.pl.
Thanks.