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SubjectRe: [PATCH RFC tip/core/rcu 15/18] rcu: give different levels of the rcu_node hierarchy distinct lockdep names
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On Tue, 2009-12-15 at 15:02 -0800, Paul E. McKenney wrote:
> From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> Proposed for 2.6.34, not for inclusion.
>
> Previously, each level of the rcu_node hierarchy had the same rather
> unimaginative name: "&rcu_node_class[i]". This makes lockdep diagnostics
> involving these lockdep classes less helpful than would be nice. This
> patch fixes this by giving each level of the rcu_node hierarchy a distinct
> name: "rcu_node_level_0", "rcu_node_level_1", and so on.
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> kernel/rcutree.c | 9 ++++++++-
> 1 files changed, 8 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 0a4c328..a6e45f6 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1811,11 +1811,17 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
> */
> static void __init rcu_init_one(struct rcu_state *rsp)
> {
> + static char *buf[] = { "rcu_node_level_0",
> + "rcu_node_level_1",
> + "rcu_node_level_2",
> + "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
> int cpustride = 1;
> int i;
> int j;
> struct rcu_node *rnp;
>
> + WARN_ON_ONCE(MAX_RCU_LVLS > 4); /* Fix buf[] initialization! */

So you're going to WARN here,

> /* Initialize the level-tracking arrays. */
>
> for (i = 1; i < NUM_RCU_LVLS; i++)
> @@ -1829,7 +1835,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
> rnp = rsp->level[i];
> for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
> spin_lock_init(&rnp->lock);
> - lockdep_set_class(&rnp->lock, &rcu_node_class[i]);
> + lockdep_set_class_and_name(&rnp->lock,
> + &rcu_node_class[i], buf[i]);

and segfault here because i overruns its bounds?

Might as well BUG_ON then.



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