On Fri, Oct 14, 2022 at 07:39:42PM +0800, Hou Tao wrote: > 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. For #2-#4: Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx> (#1 already has my Signed-off-by, in case anyone was wondering.) > 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 >
