[PATCH bpf-next v2 0/2] bpf: Migrate bpf_task_work and file dynptr to kmalloc_nolock

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

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/

---
Mykyta Yatsenko (2):
      bpf: Migrate bpf_task_work to kmalloc_nolock
      bpf: Migrate dynptr file to kmalloc_nolock

 kernel/bpf/helpers.c | 60 ++++++++++++++++++++++++++++++++++------------------
 1 file changed, 39 insertions(+), 21 deletions(-)
---
base-commit: 9f7d8fa6817e2709846fc7f5c9f60254e536d138
change-id: 20260223-kmalloc_special-933ec4c543d7

Best regards,
--  
Mykyta Yatsenko <yatsenko@meta.com>