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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-10-19 14:52:41 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-12-11 09:17:39 -0800 |
| commit | efd88b02bb9e6b8b73a20ea611e5d07ed6d4af34 (patch) | |
| tree | 0f84096dc8cc757f5c0c8b7c9de51dec0ccd9342 /kernel/rcu | |
| parent | 9122caf99b85c0f16938419547d5a9a84ae287a4 (diff) | |
rcu: Add comment giving debug strategy for double call_rcu()
The following statement has for some reason proven non-intuitive:
WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
This commit therefore adds a comment that states that this warning
usually triggers in response to a double call_rcu(), which is sort
of like a double free. The comment also suggests building with
CONFIG_DEBUG_OBJECTS_RCU_HEAD=y to track down the double call_rcu().
Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f9c0ca2ccf0c..1bdc0481aaf1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2789,6 +2789,11 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) rdp->n_force_qs_snap = rsp->n_force_qs; } else if (count < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = count; + + /* + * The following usually indicates a double call_rcu(). To track + * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. + */ WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0)); local_irq_restore(flags); |