net/dst_cache.c: preemption bug in net/dst_cache.c

[Bharath Vedartham]

Hi all,

I just want to bring attention to the syzbot bug [1]

Even though syzbot claims the bug to be in net/tipc, I feel it is in
net/dst_cache.c. Please correct me if I am wrong.

This bug is being triggered a lot of times by syzbot since the day it
was reported. Also given that this is core networking code, I felt it
was important to bring this to attention.

It looks like preemption needs to be disabled before using this_cpu_ptr
or maybe we would be better of using a get_cpu_var and put_cpu_var combo
here.

[1] https://syzkaller.appspot.com/bug?id=dc6352b92862eb79373fe03fdf9af5928753e057

Thank you
Bharath