diff options
| author | Srivatsa Vaddagiri <vatsa@in.ibm.com> | 2005-12-12 00:37:07 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-12-12 08:57:42 -0800 |
| commit | c3f5902325d3053986e7359f706581d8f032e72f (patch) | |
| tree | 1d56b7626b83556982eafad69c597b180c2ef62b /kernel | |
| parent | 89d46b8778f65223f732d82c0166e0abba20fb1e (diff) | |
| download | lwn-c3f5902325d3053986e7359f706581d8f032e72f.tar.gz lwn-c3f5902325d3053986e7359f706581d8f032e72f.zip | |
[PATCH] Fix RCU race in access of nohz_cpu_mask
Accessing nohz_cpu_mask before incrementing rcp->cur is racy. It can cause
tickless idle CPUs to be included in rsp->cpumask, which will extend
graceperiods unnecessarily.
Fix this race. It has been tested using extensions to RCU torture module
that forces various CPUs to become idle.
Signed-off-by: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/rcupdate.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index f45b91723dc6..48d3bce465b8 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -257,15 +257,23 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, if (rcp->next_pending && rcp->completed == rcp->cur) { - /* Can't change, since spin lock held. */ - cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); - rcp->next_pending = 0; - /* next_pending == 0 must be visible in __rcu_process_callbacks() - * before it can see new value of cur. + /* + * next_pending == 0 must be visible in + * __rcu_process_callbacks() before it can see new value of cur. */ smp_wmb(); rcp->cur++; + + /* + * Accessing nohz_cpu_mask before incrementing rcp->cur needs a + * Barrier Otherwise it can cause tickless idle CPUs to be + * included in rsp->cpumask, which will extend graceperiods + * unnecessarily. + */ + smp_mb(); + cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); + } } |