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markers: re-enable 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.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mathieu Desnoyers 2008-10-01 12:03:25 -04:00 committed by Ingo Molnar
parent 5b9261d93e
commit ed86a59071
1 changed files with 52 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
kernel/marker.c
View File

@ -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 marker *mdata, void *call_private, ...)
}
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(const char *name, const char *format)
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 *name)
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 marker_entry **entry, const char *format)
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 *name, const char *format,
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 *name, const char *format,
}
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 *name,
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(marker_probe_func *probe,
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);