markers: fix unregister bug and reenter bug

unregister bug:

codes using makers are typically calling marker_probe_unregister()
and then destroying the data that marker_probe_func needs(or
unloading this module). This is bug when the corresponding
marker_probe_func is still running(on other cpus),
it is using the destroying/ed data.

we should call synchronize_sched() after marker_update_probes().

reenter bug:

marker_probe_register(), marker_probe_unregister() and
marker_probe_unregister_private_data() are not reentrant safe
functions. these 3 functions release markers_mutex and then
require it again and do "entry->oldptr = old; ...", but entry->oldptr
maybe is using now for these 3 functions may reenter when markers_mutex
is released.

we use synchronize_sched() instead of call_rcu_sched() to fix
this bug. actually we can do:
"
if (entry->rcu_pending)
		rcu_barrier_sched();
"
after require markers_mutex again. but synchronize_sched()
is better and simpler. For these 3 functions are not critical path.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 6 insertions, 46 deletions

diff --git a/kernel/marker.c b/kernel/marker.c
index 7d1faecd7a51..9f76c4a622ec 100644
--- a/kernel/marker.c
+++ b/kernel/marker.c
@@ -60,9 +60,6 @@ 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' */
 };
@@ -199,16 +196,6 @@ 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;
@@ -417,7 +404,6 @@ 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;
 }
@@ -447,9 +433,6 @@ 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;
 }
@@ -479,12 +462,8 @@ 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",
@@ -658,12 +637,6 @@ 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);
@@ -671,14 +644,11 @@ 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);
-        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;
@@ -708,20 +678,15 @@ 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;
-        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:
@@ -787,19 +752,14 @@ 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);
-        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);