Messages in this thread Patch in this message | | | Date | Thu, 17 Sep 2009 22:10:01 GMT | From | "tip-bot for Paul E. McKenney" <> | Subject | [tip:core/urgent] rcu: Need to update rnp->gpnum if preemptable RCU is to be reliable |
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Commit-ID: de078d875cc7fc709f7818f26d38389c04369826 Gitweb: http://git.kernel.org/tip/de078d875cc7fc709f7818f26d38389c04369826 Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> AuthorDate: Tue, 8 Sep 2009 15:54:36 -0700 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Fri, 18 Sep 2009 00:04:54 +0200
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>
--- kernel/rcutree.c | 6 +++++- 1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6b11b07..c634a92 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. */ }
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