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SubjectRe: [BUG] Use of probe_kernel_address() in task_rcu_dereference() without checking return value
On 08/30, Linus Torvalds wrote:
> But yes, your hack is I guess optimal for this particular case where
> you simply can depend on "we know the pointer was valid, we just don't
> know if it was freed".
> Hmm. Don't we RCU-free the task struct? Because then we don't even
> need to care about CONFIG_DEBUG_PAGEALLOC. We can just always access
> the pointer as long as we have the RCU read lock.

For example,

p = task_rcu_dereference(&cpu_rq(cpu)->curr);

->curr is not protected by RCU, the last schedule does put_task_struct()
in finish_task_switch().

Of course we can change this and add another call_rcu (actually we can do
better), and after that we do not need task_rcu_dereference() at all.


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