Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

Thomas Gleixner
2020-08-11T15:43:20Z

"Paul E. McKenney" <paulmck@kernel.org> writes:
> On Tue, Aug 11, 2020 at 04:44:21PM +0200, Thomas Gleixner wrote:
>> Now RCU creates a new thing which enforces to make page allocation in
>> atomic context possible on RT. What for?
>>
>> What's the actual use case in truly atomic context for this new thing on
>> an RT kernel?
>
> It is not just RT kernels. CONFIG_PROVE_RAW_LOCK_NESTING=y propagates
> this constraint to all configurations, and a patch in your new favorite
> subsystem really did trigger this lockdep check in a non-RT kernel.
>
>> The actual RCU code disabling interrupts is an implementation detail
>> which can easily be mitigated with a local lock.
>
> In this case, we are in raw-spinlock context on entry to kfree_rcu().

Where?