Bug#988044: linux-image-5.10.0-0.bpo.4-amd64: Kernel panic due nfsd error: refcount_t: addition on 0; use-after-free

[Salvatore Bonaccorso <carnil@debian.org>]

Hi Olivier,

On Mon, Nov 22, 2021 at 09:27:26AM +0000, Olivier Monaco wrote:
> Hi Salvatore,
> 
> Sorry for my very very late answer.
> 
> I tried many actions to reproduce and/or fix this problem. We
> upgraded our kernel to the lastest backport version for Buster but
> the issue was still there. We upgraded to Bullseye at the end of
> October but today this issue occurred again. 
> 
> I think it related to https://lore.kernel.org/linux-nfs/YV3vDQOPVgxc%2FJ99@eldamar.lan/
> 
> I just send an email to this thread. 
> 
> Something that may be important: our groups of servers are used to
> host websites, some with only one website, some with many. For now,
> this issue only occurred on NFS servers part of a group with many
> websites. But one of the most loaded NFS server is also used only
> for one website and has never had this issue. May be this issue
> occurs only when the NFS server is serving many different files.

I was never able to reliably reproduce the issue myself, but upstream
now thinks to have isolated the issue and should be fixed with:

https://git.kernel.org/linus/548ec0805c399c65ed66c6641be467f717833ab5

Fixes are as well queued to stable series.

Regards,
Salvatore