Re: [PATCH -mm] markers: avoid call_rcu_sched if old is NULL

* Masami Hiramatsu (mhiramat@xxxxxxxxxx) wrote:
Introduce marker_entry_free_old() and check old pointer is NULL before
setting call_rcu_sched(), because marker_entry_remove/add_probe() can
return NULL.


Hi Masami,

I doubt this is a bug per se, because kfree accepts NULL pointers (and
kfree is the only action done on the oldptr by free_old_closure).

This cleans up the code, so I think it's good to merge your patch, but I
would definitely not classify this as a bugfix.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>

Mathieu

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
kernel/marker.c | 29 ++++++++++++++---------------
1 file changed, 14 insertions(+), 15 deletions(-)

Mathieu, I think this might be a bug. Tracepoint also has
same bug...

Index: 2.6.26-rc8-mm1/kernel/marker.c
===================================================================
--- 2.6.26-rc8-mm1.orig/kernel/marker.c 2008-07-07 11:42:04.000000000 -0400
+++ 2.6.26-rc8-mm1/kernel/marker.c 2008-07-07 11:42:04.000000000 -0400
@@ -201,6 +201,17 @@ static void free_old_closure(struct rcu_
entry->rcu_pending = 0;
}

+static void marker_entry_free_old(struct marker_entry *entry, void *old)
+{
+ if (!old)
+ return;
+ 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);
+}
+
static void debug_print_probes(struct marker_entry *entry)
{
int i;
@@ -666,11 +677,7 @@ int marker_probe_register(const char *na
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);
+ marker_entry_free_old(entry, old);
end:
mutex_unlock(&markers_mutex);
return ret;
@@ -709,11 +716,7 @@ int marker_probe_unregister(const char *
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);
+ marker_entry_free_old(entry, old);
remove_marker(name); /* Ignore busy error message */
ret = 0;
end:
@@ -787,11 +790,7 @@ int marker_probe_unregister_private_data
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);
+ marker_entry_free_old(entry, old);
remove_marker(entry->name); /* Ignore busy error message */
end:
mutex_unlock(&markers_mutex);
--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@xxxxxxxxxx


--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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