OpenE2K
/
linux
6
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

[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>
This commit is contained in:
Srivatsa Vaddagiri 2005-12-12 00:37:07 -08:00 committed by Linus Torvalds
parent 89d46b8778
commit c3f5902325
1 changed files with 13 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
kernel/rcupdate.c
View File

@ -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);
}
}