Are you planning to commit the change to mountroot?
Mike
On 20 Jul 2023, at 21:37, Mike Karels wrote:
> Mateusz Guzik wrote:
>> On 7/20/23, Mike Karels wrote:
>>> I installed an additional NVME drive on a system, and then booted. It
>>> turns
>>> out that the new drive became nda0, renumbering the other drives. The
>>> loader
>>> found the correct partition to boot (the only choice), and loaded the
>>> kernel
>>> correctly. However, /etc/fstab still had the old name (nvd1p2), which is
>>> now drive 2. I expected it to drop into single user, but instead the
>>> system
>>> panicked in vfs_mountroot_shuffle trying to switch root devices (see
>>> below).
>>> It doesn't seem that having the wrong root device in /etc/fstab should
>>> cause
>>> a panic; it makes it harder to patch the system. I was unable to get the
>>> system to boot using boot-to-single-user or setting currdev, but I managed
>>> to remember doing "boot -a" from a loader prompt to get the system to ask
>>> the root device before mounting it. I can easily reproduce this to test.
>>> Probably the NDFREE_PNBUF() shouldn't happen if namei() returned an error.
>>>
>
>> ye, this should do it (untested):
>
>> diff --git a/sys/kern/vfs_mountroot.c b/sys/kern/vfs_mountroot.c
>> index 956d29e3f084..85398ff781e4 100644
>> --- a/sys/kern/vfs_mountroot.c
>> +++ b/sys/kern/vfs_mountroot.c
>> @@ -352,13 +352,13 @@ vfs_mountroot_shuffle(struct thread *td, struct
>> mount *mpdevfs)
>> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, fspath);
>> error = namei();
>> if (error) {
>> - NDFREE_PNBUF();
>> fspath = "/mnt";
>> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE,
>> fspath);
>> error = namei();
>> }
>> if (!error) {
>> + NDFREE_PNBUF();
>> vp = nd.ni_vp;
>> error = (vp->v_type == VDIR) ? 0 : ENOTDIR;
>> if (!error)
>> @@ -376,7 +376,6 @@ vfs_mountroot_shuffle(struct thread *td, struct
>> mount *mpdevfs)
>> } else
>> vput(vp);
>> }
>> - NDFREE_PNBUF();
>
>> if (error)
>> printf("mountroot: unable to remount previous root "
>> @@ -387,6 +386,7 @@ vfs_mountroot_shuffle(struct thread *td, struct
>> mount *mpdevfs)
>> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, "/dev");
>> error = namei();
>> if (!error) {
>> + NDFREE_PNBUF();
>> vp = nd.ni_vp;
>> error = (vp->v_type == VDIR) ? 0 : ENOTDIR;
>> if (!error)
>
> That was missing the last change, and tabs were expanded. I put it in
> by hand, and the patch works, at least to avoid this panic. It still
> insisted on remounting root on nda1p2, which is not a root file system.
> Remounting /dev still failed without panicking, then it panicked because
> there was no /sbin/init. Apparently it is necessary to use "boot -a"
> in this situation. Too bad the loader option menu doesn't include that.
>
> Just to be clear what I tested, my patch follows.
>
> Mike
>
> diff --git a/sys/kern/vfs_mountroot.c b/sys/kern/vfs_mountroot.c
> index 956d29e3f084..b08b2a3200f8 100644
> --- a/sys/kern/vfs_mountroot.c
> +++ b/sys/kern/vfs_mountroot.c
> @@ -352,13 +352,13 @@ vfs_mountroot_shuffle(struct thread *td, struct mount
> *mpdevfs)
> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, fspath);
> error = namei();
> if (error) {
> - NDFREE_PNBUF();
> fspath = "/mnt";
> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE,
> fspath);
> error = namei();
> }
> if (!error) {
> + NDFREE_PNBUF();
> vp = nd.ni_vp;
> error = (vp->v_type == VDIR) ? 0 : ENOTDIR;
> if (!error)
> @@ -376,7 +376,6 @@ vfs_mountroot_shuffle(struct thread *td, struct mount
> *mpdevfs)
> } else
> vput(vp);
> }
> - NDFREE_PNBUF();
>
> if (error)
> printf("mountroot: unable to remount previous root "
> @@ -387,6 +386,7 @@ vfs_mountroot_shuffle(struct thread *td, struct mount
> *mpdevfs)
> NDINIT(, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, "/dev");
> error = namei();
> if (!error) {
> + NDFREE_PNBUF();
> vp = nd.ni_vp;
> error = (vp->v_type == VDIR) ? 0 : ENOTDIR;
> if (!error)
> @@ -413,7 +413,6 @@ vfs_mountroot_shuffle(struct thread *td, struct mount
> *mpdevfs)
> if
