Backporting 3a7956e25e1d to LTS kernels?

Backporting 3a7956e25e1d to LTS kernels?

[Jakub Jankowski]

Hi,

We've recently hit this on 5.4.124:
   WARNING: CPU: 5 PID: 35 at kernel/kthread.c:75 
kthread_is_per_cpu+0x21/0x30

After some digging, I figured out that this should be fixed by commit 
3a7956e25e1d ("kthread: Fix PF_KTHREAD vs to_kthread() race") in mainline.
It Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU")

3a7956e25e1d has been backported to 5.12.x and 5.11.x:
- 5.12.4:  as 163dd7fa459faebe055bcbebf9e088bae04f8e33
- 5.11.21: as 42e4caa93282ade6a143ff320d71062874dd3a5a

Makes sense, as ac687e6e8c26 originally landed in 5.11.

But it appears that since then ac687e6e8c26 has also been backported to 
LTS trees:
- 5.10.14:  as b20475a80b4bd2c7bc720c3a9a8337c36b20dd8c
- 5.4.96:   as 5b1e4fc2984eab30c5fffbf2bd1f016577cadab6
- 4.19.174: as fbad32181af9c8c76698b16115c28a493c26a2ee
- 4.14.220: as a9b2e4a94eee352e0b3e863045e7379d83131ee2

Maybe those trees could use a backport of 3a7956e25e1d as well then?


Cheers,
  Jakub.

Re: Backporting 3a7956e25e1d to LTS kernels?

[Greg KH]

On Thu, Jun 24, 2021 at 04:03:13AM +0200, Jakub Jankowski wrote:
> Hi,
> 
> We've recently hit this on 5.4.124:
>   WARNING: CPU: 5 PID: 35 at kernel/kthread.c:75
> kthread_is_per_cpu+0x21/0x30
> 
> After some digging, I figured out that this should be fixed by commit
> 3a7956e25e1d ("kthread: Fix PF_KTHREAD vs to_kthread() race") in mainline.
> It Fixes: ac687e6e8c26 ("kthread: Extract KTHREAD_IS_PER_CPU")
> 
> 3a7956e25e1d has been backported to 5.12.x and 5.11.x:
> - 5.12.4:  as 163dd7fa459faebe055bcbebf9e088bae04f8e33
> - 5.11.21: as 42e4caa93282ade6a143ff320d71062874dd3a5a
> 
> Makes sense, as ac687e6e8c26 originally landed in 5.11.
> 
> But it appears that since then ac687e6e8c26 has also been backported to LTS
> trees:
> - 5.10.14:  as b20475a80b4bd2c7bc720c3a9a8337c36b20dd8c
> - 5.4.96:   as 5b1e4fc2984eab30c5fffbf2bd1f016577cadab6
> - 4.19.174: as fbad32181af9c8c76698b16115c28a493c26a2ee
> - 4.14.220: as a9b2e4a94eee352e0b3e863045e7379d83131ee2
> 
> Maybe those trees could use a backport of 3a7956e25e1d as well then?

I would love to take a copy to those older trees, but the patch does not
apply to those trees.  Can you please provide a working backport that
you have tested and we will be glad to take it.

thanks,

greg k-h