Merge branch 'bpf-migrate-bpf_task_work-and-file-dynptr-to-kmalloc_nolock'

Mykyta Yatsenko says:

====================
bpf: Migrate bpf_task_work and file dynptr to kmalloc_nolock

Now that kmalloc can be used from NMI context via kmalloc_nolock(),
migrate BPF internal allocations away from bpf_mem_alloc to use the
standard slab allocator.

Use kfree_rcu() for deferred freeing, which waits for a regular RCU
grace period before the memory is reclaimed. Sleepable BPF programs
hold rcu_read_lock_trace but not regular rcu_read_lock, so patch 1
adds explicit rcu_read_lock/unlock around the pointer-to-refcount
window to prevent kfree_rcu from freeing memory while a sleepable
program is still between reading the pointer and acquiring a
reference.

Patch 1 migrates bpf_task_work_ctx from bpf_mem_alloc/bpf_mem_free to
kmalloc_nolock/kfree_rcu.

Patch 2 migrates bpf_dynptr_file_impl from bpf_mem_alloc/bpf_mem_free
to kmalloc_nolock/kfree.

Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
---
Changes in v2:
- Switch to scoped_guard in patch 1 (Kumar)
- Remove rcu gp wait in patch 2 (Kumar)
- Defer to irq_work when irqs disabled in patch 1
- use bpf_map_kmalloc_nolock() for bpf_task_work
- use kmalloc_nolock() for file dynptr
- Link to v1: https://lore.kernel.org/all/20260325-kmalloc_special-v1-0-269666afb1ea@meta.com/
====================

Link: https://patch.msgid.link/20260330-kmalloc_special-v2-0-c90403f92ff0@meta.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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