Re: [PATCH bpf-next v1 1/2] bpf: Summarize sleepable global subprogs

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2025-02-28 at 08:28 -0800, Kumar Kartikeya Dwivedi wrote:
> The verifier currently does not permit global subprog calls when a lock
> is held, preemption is disabled, or when IRQs are disabled. This is
> because we don't know whether the global subprog calls sleepable
> functions or not.
> 
> In case of locks, there's an additional reason: functions called by the
> global subprog may hold additional locks etc. The verifier won't know
> while verifying the global subprog whether it was called in context
> where a spin lock is already held by the program.
> 
> Perform summarization of the sleepable nature of a global subprog just
> like changes_pkt_data and then allow calls to global subprogs for
> non-sleepable ones from atomic context.
> 
> While making this change, I noticed that RCU read sections had no
> protection against sleepable global subprog calls, include it in the
> checks and fix this while we're at it.
> 
> Care needs to be taken to not allow global subprog calls when regular
> bpf_spin_lock is held. When resilient spin locks is held, we want to
> potentially have this check relaxed, but not for now.
> 
> Tests are included in the next patch to handle all special conditions.
> 
> Fixes: 9bb00b2895cb ("bpf: Add kfunc bpf_rcu_read_lock/unlock()")
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

I think this change also has to deal with freplace for sleepable
sub-programs, e.g. see verifier.c:bpf_check_attach_target(),
part dealing with `tgt_changes_pkt_data`.

Other than that the logic seems ok.

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