joelagnel

C srcu-impl-write-prop
(*
 * Can an SRCU reader propogate it stores to CPUs after
 * a grace period ends.
 *)

{
}

// Synchronous updater

joelagnel

C srcu
(*
 * Can SRCU satisfy grace-period ordering guarantees?
 * Case 1: Updates within writer and loads from 2 readers.
 *)

{
        int x = 1;
        int *y = &x;
        int z = 1;

joelagnel

C srcu
(*
 * Can SRCU satisfy grace-period ordering guarantees?
 * Case 2: Updates within readers.
 *)

{
        int x0 = 0; int y0 = 0; int x1 = 0; int y1 = 0;
}

joelagnel

diff --git a/drivers/ptp/ptp_kvm_x86.c b/drivers/ptp/ptp_kvm_x86.c
index 4991054a2135..4f428d104d12 100644
--- a/drivers/ptp/ptp_kvm_x86.c
+++ b/drivers/ptp/ptp_kvm_x86.c
@@ -20,7 +20,7 @@ static struct kvm_clock_pairing clock_pair;

 int kvm_arch_ptp_init(void)
 {
-       long ret;

joelagnel

C srcu
(*
 * Can SRCU satisfy grace-period ordering guarantees?
 * Case 2: writes in critical section, reads in updater
 *)

{
        int x = 0; int y = 0;
}

joelagnel

C srcu
(*
 * Can SRCU satisfy grace-period ordering guarantees?
 * Case 1: Updates are seen properly in reader.
 *)

{
int x = 1;
int *y = &x;
int z = 1;

joelagnel

Kernel Debugging Tricks

Introduction

Debugging the kernel is a difficult task. Thankfully there are quite a few built-in kernel debugging tools and techniques that help one quickly identify the source and/or the cause of an issue.

Enable debug information

joelagnel

Ordering of class-balancing with put-prev-task

During a context switch, the schedule() loop calls the class-level pick_next_task() to find the next task to run on the CPU.

It looks something like this:

First schedule() calls pick_next_task() passing it the previous task as shown in \ref{lst:rq2}.

joelagnel

/* Here is the output of below module:
[    3.069018] rd1: rwsem read acquired
[    3.276624] wr1: about to acquire     // Writer blocked on lock before..
[    4.107213] rd2: about to acquire     // ..the 2nd reader blocked on it.
[    6.154863] rd1: rwsem read released
[    6.155651] wr1: rwsem write acquired // Writer got the lock first.
[    6.362821] wr1: rwsem write released
[    6.363150] rd2: rwsem read acquired  // Then new reader got it.
[    6.578677] rd2: msleep done

joelagnel

use std::sync::{Arc, Mutex};
use std::thread;
use std::thread::JoinHandle;
use std::fs;

fn debug(msg: &str) {
    println!("{}", msg);
    _ = fs::write("/sys/kernel/debug/tracing/trace_marker", msg);
}