From: Hou Tao <houtao1@xxxxxxxxxx> Hi, Now bpf uses RCU grace period chaining to wait for the completion of access from both sleepable and non-sleepable bpf program: calling call_rcu_tasks_trace() firstly to wait for a RCU-tasks-trace grace period, then in its callback calls call_rcu() or kfree_rcu() to wait for a normal RCU grace period. According to the implementation of RCU Tasks Trace, it inovkes ->postscan_func() to wait for one RCU-tasks-trace grace period and rcu_tasks_trace_postscan() inovkes synchronize_rcu() to wait for one normal RCU grace period in turn, so one RCU-tasks-trace grace period will imply one normal RCU grace period. To codify the implication, introduces rcu_trace_implies_rcu_gp() in patch #1. And using it in patch #2~#4 to remove unnecessary call_rcu() or kfree_rcu() in bpf subsystem. Other two uses of call_rcu_tasks_trace() are unchanged: for __bpf_prog_put_rcu() there is no gp chain and for __bpf_tramp_image_put_rcu_tasks() it chains RCU tasks trace GP and RCU tasks GP. An alternative way to remove these unnecessary RCU grace period chainings is using the RCU polling API to check whether or not a normal RCU grace period has passed (e.g. get_state_synchronize_rcu()). But it needs an unsigned long space for each free element or each call, and it is not affordable for local storage element, so as for now always rcu_trace_implies_rcu_gp(). Comments are always welcome. Change Log: v2: * codify the implication of RCU Tasks Trace grace period instead of assuming for it v1: https://lore.kernel.org/bpf/20221011071128.3470622-1-houtao@xxxxxxxxxxxxxxx Hou Tao (3): bpf: Use rcu_trace_implies_rcu_gp() in bpf memory allocator bpf: Use rcu_trace_implies_rcu_gp() in local storage map bpf: Use rcu_trace_implies_rcu_gp() for program array freeing Paul E. McKenney (1): rcu-tasks: Provide rcu_trace_implies_rcu_gp() include/linux/rcupdate.h | 12 ++++++++++++ kernel/bpf/bpf_local_storage.c | 13 +++++++++++-- kernel/bpf/core.c | 8 +++++++- kernel/bpf/memalloc.c | 15 ++++++++++----- kernel/rcu/tasks.h | 2 ++ 5 files changed, 42 insertions(+), 8 deletions(-) -- 2.29.2
