| Message ID | 20210624160609.292325-1-toke@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Clean up and document RCU-based object protection for XDP and TC BPF | expand |
Hello: This series was applied to bpf/bpf-next.git (refs/heads/master): On Thu, 24 Jun 2021 18:05:50 +0200 you wrote: > During the discussion[0] of Hangbin's multicast patch series, Martin pointed out > that the lifetime of the RCU-protected map entries used by XDP_REDIRECT is by > no means obvious. I promised to look into cleaning this up, and Paul helpfully > provided some hints and a new unrcu_pointer() helper to aid in this. > > It seems[1] that back in the early days of XDP, local_bh_disable() did not > provide RCU protection, which is why the rcu_read_lock() calls were added > to drivers in the first place. But according to Paul[2], in recent kernels > a local_bh_disable()/local_bh_enable() pair functions as one big RCU > read-side section, so no further protection is needed. This even applies to > -rt kernels, which has an explicit rcu_read_lock() in place as part of the > local_bh_disable()[3]. > > [...] Here is the summary with links: - [bpf-next,v5,01/19] rcu: Create an unrcu_pointer() to remove __rcu from a pointer https://git.kernel.org/bpf/bpf-next/c/b9964ce74544 - [bpf-next,v5,02/19] doc: Clarify and expand RCU updaters and corresponding readers https://git.kernel.org/bpf/bpf-next/c/9a145c04a293 - [bpf-next,v5,03/19] doc: Give XDP as example of non-obvious RCU reader/updater pairing https://git.kernel.org/bpf/bpf-next/c/e74c74f9e51d - [bpf-next,v5,04/19] bpf: allow RCU-protected lookups to happen from bh context https://git.kernel.org/bpf/bpf-next/c/694cea395fde - [bpf-next,v5,05/19] xdp: add proper __rcu annotations to redirect map entries https://git.kernel.org/bpf/bpf-next/c/782347b6bcad - [bpf-next,v5,06/19] sched: remove unneeded rcu_read_lock() around BPF program invocation https://git.kernel.org/bpf/bpf-next/c/77151ccf1065 - [bpf-next,v5,07/19] ena: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/0939e0537896 - [bpf-next,v5,08/19] bnxt: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/158c1399fc45 - [bpf-next,v5,09/19] thunderx: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/36baafe347a8 - [bpf-next,v5,10/19] freescale: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/547aabcac325 - [bpf-next,v5,11/19] net: intel: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/49589b23d5a9 - [bpf-next,v5,12/19] marvell: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/959ad7ec066d - [bpf-next,v5,13/19] mlx4: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/c4411b371c10 - [bpf-next,v5,14/19] nfp: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/d5789621b658 - [bpf-next,v5,15/19] qede: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/4415db6ca85a - [bpf-next,v5,16/19] sfc: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/4eb14e3fc619 - [bpf-next,v5,17/19] netsec: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/7b6ee873ff20 - [bpf-next,v5,18/19] stmmac: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/2f1e432d339c - [bpf-next,v5,19/19] net: ti: remove rcu_read_lock() around XDP program invocation https://git.kernel.org/bpf/bpf-next/c/0cc84b9a6003 You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
During the discussion[0] of Hangbin's multicast patch series, Martin pointed out that the lifetime of the RCU-protected map entries used by XDP_REDIRECT is by no means obvious. I promised to look into cleaning this up, and Paul helpfully provided some hints and a new unrcu_pointer() helper to aid in this. It seems[1] that back in the early days of XDP, local_bh_disable() did not provide RCU protection, which is why the rcu_read_lock() calls were added to drivers in the first place. But according to Paul[2], in recent kernels a local_bh_disable()/local_bh_enable() pair functions as one big RCU read-side section, so no further protection is needed. This even applies to -rt kernels, which has an explicit rcu_read_lock() in place as part of the local_bh_disable()[3]. This patch series is mostly a documentation exercise, cleaning up the description of the lifetime expectations and adding __rcu annotations so sparse and lockdep can help verify it. Patches 1-4 are preparatory: Patch 1 adds Paul's unrcu_pointer() helper (which has already been added to his tree), which we need for some of the operations in devmap, patches 2 and 3 update the RCU documentation and patch 4 adds bh context as a valid condition for map lookups. Patch 5 is the main bit that adds the __rcu annotations and updates documentation comments. Finally, patch 6 removes unneeded rcu_read_lock()s from TC BPF, and the rest are patches updating the drivers, with one patch per distinct maintainer. Unfortunately I don't have any hardware to test any of the driver patches; Jesper helpfully verified that it doesn't break anything on i40e, but the rest of the driver patches are only compile-tested. [0] https://lore.kernel.org/bpf/20210415173551.7ma4slcbqeyiba2r@kafai-mbp.dhcp.thefacebook.com/ [1] https://lore.kernel.org/bpf/c5192ab3-1c05-8679-79f2-59d98299095b@iogearbox.net/ [2] https://lore.kernel.org/bpf/20210417002301.GO4212@paulmck-ThinkPad-P17-Gen-1/ [3] https://lore.kernel.org/bpf/20210419165837.GA975577@paulmck-ThinkPad-P17-Gen-1/ Changelog: v5: - Rebase to bpf-next and fix build error v4: - Move comment about RCU protection into core instead of leaving it in drivers - Also remove rcu_read_lock() around TC BPF program execution - Fold in a couple of patches from Paul updating the RCU documentation v3: - Remove one other unnecessary change to hlist_for_each_entry_rcu() - Carry forward another ACK v2: - Add a comment about RCU protection to the drivers where rcu_read_lock() is removed - Drop unnecessary patch 3 which changed dev_get_by_index_rcu() - Add some more text with the history to cover letter - Fix a few places where the wrong RCU checks were used in cpumap and xskmap code - Carry forward ACKs Paul E. McKenney (2): rcu: Create an unrcu_pointer() to remove __rcu from a pointer doc: Clarify and expand RCU updaters and corresponding readers Toke Høiland-Jørgensen (17): doc: Give XDP as example of non-obvious RCU reader/updater pairing bpf: allow RCU-protected lookups to happen from bh context xdp: add proper __rcu annotations to redirect map entries sched: remove unneeded rcu_read_lock() around BPF program invocation ena: remove rcu_read_lock() around XDP program invocation bnxt: remove rcu_read_lock() around XDP program invocation thunderx: remove rcu_read_lock() around XDP program invocation freescale: remove rcu_read_lock() around XDP program invocation net: intel: remove rcu_read_lock() around XDP program invocation marvell: remove rcu_read_lock() around XDP program invocation mlx4: remove rcu_read_lock() around XDP program invocation nfp: remove rcu_read_lock() around XDP program invocation qede: remove rcu_read_lock() around XDP program invocation sfc: remove rcu_read_lock() around XDP program invocation netsec: remove rcu_read_lock() around XDP program invocation stmmac: remove rcu_read_lock() around XDP program invocation net: ti: remove rcu_read_lock() around XDP program invocation Documentation/RCU/checklist.rst | 55 ++++++++++++------- drivers/net/ethernet/amazon/ena/ena_netdev.c | 3 - drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 2 - .../net/ethernet/cavium/thunder/nicvf_main.c | 2 - .../net/ethernet/freescale/dpaa/dpaa_eth.c | 8 +-- .../net/ethernet/freescale/dpaa2/dpaa2-eth.c | 3 - drivers/net/ethernet/intel/i40e/i40e_txrx.c | 2 - drivers/net/ethernet/intel/i40e/i40e_xsk.c | 3 - drivers/net/ethernet/intel/ice/ice_txrx.c | 6 +- drivers/net/ethernet/intel/ice/ice_xsk.c | 3 - drivers/net/ethernet/intel/igb/igb_main.c | 2 - drivers/net/ethernet/intel/igc/igc_main.c | 7 +-- drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 2 - drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 3 - .../net/ethernet/intel/ixgbevf/ixgbevf_main.c | 2 - drivers/net/ethernet/marvell/mvneta.c | 2 - .../net/ethernet/marvell/mvpp2/mvpp2_main.c | 4 -- drivers/net/ethernet/mellanox/mlx4/en_rx.c | 8 +-- .../ethernet/netronome/nfp/nfp_net_common.c | 2 - drivers/net/ethernet/qlogic/qede/qede_fp.c | 6 -- drivers/net/ethernet/sfc/rx.c | 9 +-- drivers/net/ethernet/socionext/netsec.c | 3 - .../net/ethernet/stmicro/stmmac/stmmac_main.c | 10 +--- drivers/net/ethernet/ti/cpsw_priv.c | 10 +--- include/linux/filter.h | 8 +-- include/linux/rcupdate.h | 14 +++++ include/net/xdp_sock.h | 2 +- kernel/bpf/cpumap.c | 13 +++-- kernel/bpf/devmap.c | 49 +++++++---------- kernel/bpf/hashtab.c | 21 ++++--- kernel/bpf/helpers.c | 6 +- kernel/bpf/lpm_trie.c | 6 +- net/core/filter.c | 28 ++++++++++ net/sched/act_bpf.c | 2 - net/sched/cls_bpf.c | 3 - net/xdp/xsk.c | 4 +- net/xdp/xsk.h | 4 +- net/xdp/xskmap.c | 29 ++++++---- 38 files changed, 164 insertions(+), 182 deletions(-)