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Subject[patch 1/5] Markers reenable fast batch registration
Lai Jiangshan discovered a reentrancy issue with markers and fixed it by adding
synchronize_sched() calls at each registration/unregistraiton. It works, but it
removes the ability to do batch registration/unregistration and can cause
registration of ~100 markers to take about 30 seconds on a loaded machine
(synchronize_sched() is much slower on such workloads). This patch implements a
version of the fix which won't slow down marker batch
registration/unregistration. It also go back to the original non-synchronized
reg/unreg, and thus needs the following
markers-synchronize_marker_unregister.patch patch and friends.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
CC: Ingo Molnar <mingo@elte.hu>
---
kernel/marker.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 52 insertions(+), 6 deletions(-)
Index: linux-2.6-lttng/kernel/marker.c
===================================================================
--- linux-2.6-lttng.orig/kernel/marker.c 2008-10-01 11:53:42.000000000 -0400
+++ linux-2.6-lttng/kernel/marker.c 2008-10-01 11:54:10.000000000 -0400
@@ -60,6 +60,9 @@ struct marker_entry {
struct marker_probe_closure single;
struct marker_probe_closure *multi;
int refcount; /* Number of times armed. 0 if disarmed. */
+ struct rcu_head rcu;
+ void *oldptr;
+ unsigned char rcu_pending:1;
unsigned char ptype:1;
char name[0]; /* Contains name'\0'format'\0' */
};
@@ -196,6 +199,16 @@ void marker_probe_cb_noarg(const struct
}
EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);

+static void free_old_closure(struct rcu_head *head)
+{
+ struct marker_entry *entry = container_of(head,
+ struct marker_entry, rcu);
+ kfree(entry->oldptr);
+ /* Make sure we free the data before setting the pending flag to 0 */
+ smp_wmb();
+ entry->rcu_pending = 0;
+}
+
static void debug_print_probes(struct marker_entry *entry)
{
int i;
@@ -404,6 +417,7 @@ static struct marker_entry *add_marker(c
e->multi = NULL;
e->ptype = 0;
e->refcount = 0;
+ e->rcu_pending = 0;
hlist_add_head(&e->hlist, head);
return e;
}
@@ -433,6 +447,9 @@ static int remove_marker(const char *nam
if (e->single.func != __mark_empty_function)
return -EBUSY;
hlist_del(&e->hlist);
+ /* Make sure the call_rcu has been executed */
+ if (e->rcu_pending)
+ rcu_barrier_sched();
kfree(e);
return 0;
}
@@ -462,8 +479,12 @@ static int marker_set_format(struct mark
e->multi = (*entry)->multi;
e->ptype = (*entry)->ptype;
e->refcount = (*entry)->refcount;
+ e->rcu_pending = 0;
hlist_add_before(&e->hlist, &(*entry)->hlist);
hlist_del(&(*entry)->hlist);
+ /* Make sure the call_rcu has been executed */
+ if ((*entry)->rcu_pending)
+ rcu_barrier_sched();
kfree(*entry);
*entry = e;
trace_mark(core_marker_format, "name %s format %s",
@@ -637,6 +658,12 @@ int marker_probe_register(const char *na
goto end;
}
}
+ /*
+ * If we detect that a call_rcu is pending for this marker,
+ * make sure it's executed now.
+ */
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
old = marker_entry_add_probe(entry, probe, probe_private);
if (IS_ERR(old)) {
ret = PTR_ERR(old);
@@ -644,11 +671,16 @@ int marker_probe_register(const char *na
}
mutex_unlock(&markers_mutex);
marker_update_probes(); /* may update entry */
- synchronize_sched();
- kfree(old);
mutex_lock(&markers_mutex);
entry = get_marker(name);
WARN_ON(!entry);
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ entry->oldptr = old;
+ entry->rcu_pending = 1;
+ /* write rcu_pending before calling the RCU callback */
+ smp_wmb();
+ call_rcu_sched(&entry->rcu, free_old_closure);
end:
mutex_unlock(&markers_mutex);
return ret;
@@ -678,15 +710,22 @@ int marker_probe_unregister(const char *
entry = get_marker(name);
if (!entry)
goto end;
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
old = marker_entry_remove_probe(entry, probe, probe_private);
mutex_unlock(&markers_mutex);
marker_update_probes(); /* may update entry */
- synchronize_sched();
- kfree(old);
mutex_lock(&markers_mutex);
entry = get_marker(name);
if (!entry)
goto end;
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ entry->oldptr = old;
+ entry->rcu_pending = 1;
+ /* write rcu_pending before calling the RCU callback */
+ smp_wmb();
+ call_rcu_sched(&entry->rcu, free_old_closure);
remove_marker(name); /* Ignore busy error message */
ret = 0;
end:
@@ -752,14 +791,21 @@ int marker_probe_unregister_private_data
ret = -ENOENT;
goto end;
}
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
old = marker_entry_remove_probe(entry, NULL, probe_private);
mutex_unlock(&markers_mutex);
marker_update_probes(); /* may update entry */
- synchronize_sched();
- kfree(old);
mutex_lock(&markers_mutex);
entry = get_marker_from_private_data(probe, probe_private);
WARN_ON(!entry);
+ if (entry->rcu_pending)
+ rcu_barrier_sched();
+ entry->oldptr = old;
+ entry->rcu_pending = 1;
+ /* write rcu_pending before calling the RCU callback */
+ smp_wmb();
+ call_rcu_sched(&entry->rcu, free_old_closure);
remove_marker(entry->name); /* Ignore busy error message */
end:
mutex_unlock(&markers_mutex);
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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