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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2020-10-01 21:27:57 -0400
committerPeter Zijlstra <peterz@infradead.org>2020-10-02 21:18:25 +0200
commit547305a64632813286700cb6d768bfe773df7d19 (patch)
tree5794b5f95a015645070022512939a324b8a84100 /kernel/tracepoint.c
parentde394e7568ce2cdb4643ed230169f484f25f9442 (diff)
tracepoint: Fix out of sync data passing by static caller
Naresh reported a bug that appears to be a side effect of the static calls. It happens when going from more than one tracepoint callback to a single one, and removing the first callback on the list. The list of tracepoint callbacks holds data and a function to call with the parameters of that tracepoint and a handler to the associated data. old_list: 0: func = foo; data = NULL; 1: func = bar; data = &bar_struct; new_list: 0: func = bar; data = &bar_struct; CPU 0 CPU 1 ----- ----- tp_funcs = old_list; tp_static_caller = tp_interator __DO_TRACE() data = tp_funcs[0].data = NULL; tp_funcs = new_list; tracepoint_update_call() tp_static_caller = tp_funcs[0] = bar; tp_static_caller(data) bar(data) x = data->item = NULL->item BOOM! To solve this, add a tracepoint_synchronize_unregister() between changing tp_funcs and updating the static tracepoint, that does both a synchronize_rcu() and synchronize_srcu(). This will ensure that when the static call is updated to the single callback that it will be receiving the data that it registered with. Fixes: d25e37d89dd2f ("tracepoint: Optimize using static_call()") Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/linux-next/CA+G9fYvPXVRO0NV7yL=FxCmFEMYkCwdz7R=9W+_votpT824YJA@mail.gmail.com
Diffstat (limited to 'kernel/tracepoint.c')
-rw-r--r--kernel/tracepoint.c22
1 files changed, 16 insertions, 6 deletions
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index e92f3fb8887a..26efd22f0633 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -221,7 +221,7 @@ static void *func_remove(struct tracepoint_func **funcs,
return old;
}
-static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs)
+static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func *tp_funcs, bool sync)
{
void *func = tp->iterator;
@@ -229,8 +229,17 @@ static void tracepoint_update_call(struct tracepoint *tp, struct tracepoint_func
if (!tp->static_call_key)
return;
- if (!tp_funcs[1].func)
+ if (!tp_funcs[1].func) {
func = tp_funcs[0].func;
+ /*
+ * If going from the iterator back to a single caller,
+ * we need to synchronize with __DO_TRACE to make sure
+ * that the data passed to the callback is the one that
+ * belongs to that callback.
+ */
+ if (sync)
+ tracepoint_synchronize_unregister();
+ }
__static_call_update(tp->static_call_key, tp->static_call_tramp, func);
}
@@ -265,7 +274,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
* include/linux/tracepoint.h using rcu_dereference_sched().
*/
rcu_assign_pointer(tp->funcs, tp_funcs);
- tracepoint_update_call(tp, tp_funcs);
+ tracepoint_update_call(tp, tp_funcs, false);
static_key_enable(&tp->key);
release_probes(old);
@@ -297,11 +306,12 @@ static int tracepoint_remove_func(struct tracepoint *tp,
tp->unregfunc();
static_key_disable(&tp->key);
+ rcu_assign_pointer(tp->funcs, tp_funcs);
} else {
- tracepoint_update_call(tp, tp_funcs);
+ rcu_assign_pointer(tp->funcs, tp_funcs);
+ tracepoint_update_call(tp, tp_funcs,
+ tp_funcs[0].func != old[0].func);
}
-
- rcu_assign_pointer(tp->funcs, tp_funcs);
release_probes(old);
return 0;
}