Re: [PATCH] Revert "riscv: kdump: fix crashkernel reserving problem on RISC-V"

[Baoquan He <bhe@redhat.com>]

On 04/19/24 at 10:55pm, Mingzheng Xing wrote:
> On 4/19/24 21:58, Greg Kroah-Hartman wrote:
> > On Fri, Apr 19, 2024 at 08:26:07PM +0800, Mingzheng Xing wrote:
> >> On 4/19/24 18:44, Greg Kroah-Hartman wrote:
> >>> On Tue, Apr 16, 2024 at 04:56:47PM +0800, Mingzheng Xing wrote:
> >>>> This reverts commit 1d6cd2146c2b58bc91266db1d5d6a5f9632e14c0 which has been
> >>>> merged into the mainline commit 39365395046f ("riscv: kdump: use generic
> >>>> interface to simplify crashkernel reservation"), but the latter's series of
> >>>> patches are not included in the 6.6 branch.
> >>>>
> >>>> This will result in the loss of Crash kernel data in /proc/iomem, and kdump
> >>>> loading the kernel will also cause an error:
> >>>>
> >>>> ```
> >>>> Memory for crashkernel is not reserved
> >>>> Please reserve memory by passing"crashkernel=Y@X" parameter to kernel
> >>>> Then try to loading kdump kernel
> >>>> ```
> >>>>
> >>>> After revert this patch, verify that it works properly on QEMU riscv.
> >>>>
> >>>> Link: https://lore.kernel.org/linux-riscv/ZSiQRDGLZk7lpakE@MiWiFi-R3L-srv
> >>>> Signed-off-by: Mingzheng Xing <xingmingzheng@iscas.ac.cn>
> >>>> ---
> >>>
> >>> I do not understand, what branch is this for?  Why have you not cc:ed
> >>> any of the original developers here?  Why does Linus's tree not have the
> >>> same problem?  And the first sentence above does not make much sense as
> >>> a 6.6 change is merged into 6.7?
> >>
> >> Sorry, I'll try to explain it more clearly.
> >>
> >> This commit 1d6cd2146c2b ("riscv: kdump: fix crashkernel reserving problem
> >> on RISC-V") should not have existed because this patch has been merged into
> >> another larger patch [1]. Here is that complete series:
> > 
> > What "larger patch"?  It is in Linus's tree, so it's not part of
> > something different, right?  I'm confused.
> > 
> 
> Hi, Greg
> 
> The email Cc:ed to author Chen Jiahao was bounced by the system, so maybe
> we can wait for Baoquan He to confirm.
> 
> This is indeed a bit confusing. The Fixes: tag in 1d6cd2146c2b58 is a false
> reference. If I understand correctly, this is similar to the following
> scenario:
> 
> A Fixes B, B doesn't go into linus mainline. C contains A, C goes into linus
> mainline 6.7, and C has more reconstruction code. but A goes into 6.6, so
> it doesn't make sense for A to be in the mainline, and there's no C in 6.6
> but there's an A, thus resulting in an incomplete code that creates an error.

Do you mean commit 1d6cd2146c2b58 ("iscv: kdump: fix crashkernel reserving
problem on RISC-V") was mistakenly added into v6.6, but the commit which
it fixed is not existing in v6.6?

I checked code, it does look like what you said, and it's truly
confusing. If so, we should revert commit 1d6cd2146c2b58 ("iscv: kdump: fix
crashkernel reserving problem on RISC-V") in v6.6.y to make kdump work
on risc-v.