Messages in this thread Patch in this message | | | From | Byungchul Park <> | Subject | [RFC] rcu: Prevent expedite reporting within RCU read-side section | Date | Tue, 6 Mar 2018 14:31:58 +0900 |
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Hello Paul and RCU folks,
I am afraid I correctly understand and fix it. But I really wonder why sync_rcu_exp_handler() reports the quiescent state even in the case that current task is within a RCU read-side section. Do I miss something?
If I correctly understand it and you agree with it, I can add more logic which make it more expedited by boosting current or making it urgent when we fail to report the quiescent state on the IPI.
----->8----- From 0b0191f506c19ce331a1fdb7c2c5a00fb23fbcf2 Mon Sep 17 00:00:00 2001 From: Byungchul Park <byungchul.park@lge.com> Date: Tue, 6 Mar 2018 13:54:41 +0900 Subject: [RFC] rcu: Prevent expedite reporting within RCU read-side section
We report the quiescent state for this cpu if it's out of RCU read-side section at the moment IPI was just fired during the expedite process.
However, current code reports the quiescent state even in the case:
1) the current task is still within a RCU read-side section 2) the current task has been blocked within the RCU read-side section
Since we don't get to the quiescent state yet in the case, we shouldn't report it but check it another time.
Signed-off-by: Byungchul Park <byungchul.park@lge.com> --- kernel/rcu/tree_exp.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 73e1d3d..cc69d14 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -731,13 +731,13 @@ static void sync_rcu_exp_handler(void *info) /* * We are either exiting an RCU read-side critical section (negative * values of t->rcu_read_lock_nesting) or are not in one at all - * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU - * read-side critical section that blocked before this expedited - * grace period started. Either way, we can immediately report - * the quiescent state. + * (zero value of t->rcu_read_lock_nesting). We can immediately + * report the quiescent state. */ - rdp = this_cpu_ptr(rsp->rda); - rcu_report_exp_rdp(rsp, rdp, true); + if (t->rcu_read_lock_nesting <= 0) { + rdp = this_cpu_ptr(rsp->rda); + rcu_report_exp_rdp(rsp, rdp, true); + } } /** -- 1.9.1
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