Peter, On Sat, Oct 17, 2015 at 2:56 AM, Peter Zijlstra <[email protected]> wrote: > > On Sat, Oct 17, 2015 at 03:28:11AM +0200, Stephane Eranian wrote: > > > > This patch eliminates all known RCU violations detected > > by the RCU checker (PROVE_RCU). The impact code paths > > were all related to cgroup mode monitoring and involved > > access a task's cgrp. > > But were they right? This patch provides no clues. > I am assuming that is the checker detects something suspicious there is likely a problem.
Take for instance: perf_cgroup_sched_out()->perf_cgroup_from_task() ->task_subsys_state() That one fires the checker. I think because we are accessing the css state without protection. The other places are similar. I am also trying to avoid double taking the rcu-read-lock(), so I have moved the rcu_read_lock() out of some functions to place them in the caller. The perf_cgroup_switch() is a performance sensitive path. If this is not the way to fix this, let me know and I'll rewrite the patch. Thanks. > > Signed-off-by: Stephane Eranian <[email protected]> > > --- > > > @@ -2094,6 +2104,7 @@ static int __perf_install_in_context(void *info) > > cpuctx->task_ctx = task_ctx; > > task = task_ctx->task; > > } > > + rcu_read_lock(); > > > > cpu_ctx_sched_out(cpuctx, EVENT_ALL); > > > > @@ -2112,6 +2123,8 @@ static int __perf_install_in_context(void *info) > > */ > > perf_event_sched_in(cpuctx, task_ctx, task); > > > > + rcu_read_unlock(); > > + > > perf_pmu_enable(cpuctx->ctx.pmu); > > perf_ctx_unlock(cpuctx, task_ctx); > > > > @@ -2398,7 +2411,9 @@ static void ctx_sched_out(struct perf_event_context > > *ctx, > > return; > > > > update_context_time(ctx); > > + rcu_read_lock(); > > update_cgrp_time_from_cpuctx(cpuctx); > > + rcu_read_unlock(); > > if (!ctx->nr_active) > > return; > > > > And these impact !cgroup code, and the last looks like it should be > inside update_cgrp_time_from_cpuctx() if at all. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
