Re: [PATCH v2 5/8] riscv: mm: Take memory hotplug read-lock during kernel page table dump

[Oscar Salvador]

On Tue, May 14, 2024 at 04:04:43PM +0200, Björn Töpel wrote:
> From: Björn Töpel <bjorn@xxxxxxxxxxxx>
> 
> During memory hot remove, the ptdump functionality can end up touching
> stale data. Avoid any potential crashes (or worse), by holding the
> memory hotplug read-lock while traversing the page table.
> 
> This change is analogous to arm64's commit bf2b59f60ee1 ("arm64/mm:
> Hold memory hotplug lock while walking for kernel page table dump").
> 
> Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

funny enough, it seems arm64 and riscv are the only ones holding the
hotplug lock here.
I think we have the same problem on the other arches as well (at least
on x86_64 that I can see).

If we happen to finally need the lock in those, I would rather have a
centric function in the generic mm code with the locking and then
calling an arch specific ptdump_show function, so the lock is not
scattered. But that is another story.

 

-- 
Oscar Salvador
SUSE Labs