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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-09-08 15:54:36 -0700
committerIngo Molnar <mingo@elte.hu>2009-09-18 00:04:54 +0200
commitde078d875cc7fc709f7818f26d38389c04369826 (patch)
tree0e7ed4d9d11ae707cc3b4e1e9d511a6d78e9e29d /kernel
parentde55a8958f6e3ef5ce5f0971b80bd44bfcac7cf1 (diff)
rcu: Need to update rnp->gpnum if preemptable RCU is to be reliable
Without this patch, tasks preempted in RCU read-side critical sections can fail to block the grace period, given that rnp->gpnum is used to determine which rnp->blocked_tasks[] element the preempted task is enqueued on. Before the patch, rnp->gpnum is always zero, so preempted tasks are always enqueued on rnp->blocked_tasks[0], which is correct only when the current CPU has not checked into the current grace period and the grace-period number is even, or, similarly, if the current CPU -has- checked into the current grace period and the grace-period number is odd. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josht@linux.vnet.ibm.com Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org LKML-Reference: <12524504771622-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcutree.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6b11b07cfe7..c634a92d121 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -632,6 +632,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
/* Special-case the common single-level case. */
if (NUM_RCU_NODES == 1) {
rnp->qsmask = rnp->qsmaskinit;
+ rnp->gpnum = rsp->gpnum;
rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
spin_unlock_irqrestore(&rnp->lock, flags);
return;
@@ -657,8 +658,10 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
*/
rnp_end = rsp->level[NUM_RCU_LVLS - 1];
- for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++)
+ for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) {
rnp_cur->qsmask = rnp_cur->qsmaskinit;
+ rnp->gpnum = rsp->gpnum;
+ }
/*
* Now set up the leaf nodes. Here we must be careful. First,
@@ -679,6 +682,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
for (; rnp_cur < rnp_end; rnp_cur++) {
spin_lock(&rnp_cur->lock); /* irqs already disabled. */
rnp_cur->qsmask = rnp_cur->qsmaskinit;
+ rnp->gpnum = rsp->gpnum;
spin_unlock(&rnp_cur->lock); /* irqs already disabled. */
}