mbox series

[bpf-next,v2,0/5] Make struct bpf_cpumask RCU safe

Message ID 20230316054028.88924-1-void@manifault.com
Headers
Series Make struct bpf_cpumask RCU safe |

Message

David Vernet March 16, 2023, 5:40 a.m. UTC 
  The struct bpf_cpumask type is currently not RCU safe. It uses the
bpf_mem_cache_{alloc,free}() APIs to allocate and release cpumasks, and
those allocations may be reused before an RCU grace period has elapsed.
We want to be able to enable using this pattern in BPF programs:

private(MASK) static struct bpf_cpumask __kptr *global;

int BPF_PROG(prog, ...)
{
	struct bpf_cpumask *cpumask;

	bpf_rcu_read_lock();
	cpumask = global;
	if (!cpumask) {
		bpf_rcu_read_unlock();
		return -1;
	}
	bpf_cpumask_setall(cpumask);
	...
	bpf_rcu_read_unlock();
}

In other words, to be able to pass a kptr to KF_RCU bpf_cpumask kfuncs
without requiring the acquisition and release of refcounts using
bpf_cpumask_kptr_get(). This patchset enables this by making the struct
bpf_cpumask type RCU safe, and removing the bpf_cpumask_kptr_get()
function.

---
v1: https://lore.kernel.org/all/20230316014122.678082-2-void@manifault.com/

Changelog:
----------
v1 -> v2:
- Add doxygen comment for new @rcu field in struct bpf_cpumask.

David Vernet (5):
  bpf: Free struct bpf_cpumask in call_rcu handler
  bpf: Mark struct bpf_cpumask as rcu protected
  bpf/selftests: Test using global cpumask kptr with RCU
  bpf: Remove bpf_cpumask_kptr_get() kfunc
  bpf,docs: Remove bpf_cpumask_kptr_get() from documentation

 Documentation/bpf/cpumasks.rst                | 30 +++-----
 kernel/bpf/cpumask.c                          | 38 +++--------
 kernel/bpf/verifier.c                         |  1 +
 .../selftests/bpf/prog_tests/cpumask.c        |  2 +-
 .../selftests/bpf/progs/cpumask_common.h      |  7 +-
 .../selftests/bpf/progs/cpumask_failure.c     | 68 +++++++++++++++----
 .../selftests/bpf/progs/cpumask_success.c     | 29 ++++----
 7 files changed, 96 insertions(+), 79 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org March 16, 2023, 7:40 p.m. UTC | #1 
Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Thu, 16 Mar 2023 00:40:23 -0500 you wrote:
> The struct bpf_cpumask type is currently not RCU safe. It uses the
> bpf_mem_cache_{alloc,free}() APIs to allocate and release cpumasks, and
> those allocations may be reused before an RCU grace period has elapsed.
> We want to be able to enable using this pattern in BPF programs:
> 
> private(MASK) static struct bpf_cpumask __kptr *global;
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/5] bpf: Free struct bpf_cpumask in call_rcu handler
    https://git.kernel.org/bpf/bpf-next/c/77473d1a962f
  - [bpf-next,v2,2/5] bpf: Mark struct bpf_cpumask as rcu protected
    https://git.kernel.org/bpf/bpf-next/c/63d2d83d21a6
  - [bpf-next,v2,3/5] bpf/selftests: Test using global cpumask kptr with RCU
    https://git.kernel.org/bpf/bpf-next/c/a5a197df58c4
  - [bpf-next,v2,4/5] bpf: Remove bpf_cpumask_kptr_get() kfunc
    https://git.kernel.org/bpf/bpf-next/c/1b403ce77dfb
  - [bpf-next,v2,5/5] bpf,docs: Remove bpf_cpumask_kptr_get() from documentation
    https://git.kernel.org/bpf/bpf-next/c/fec2c6d14fd5

You are awesome, thank you!