Messages in this thread |  | | Date | Thu, 31 Oct 2013 19:16:54 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer |
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On 10/29, Namhyung Kim wrote: > > @@ -630,6 +653,19 @@ probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter) > if (trace_probe_is_enabled(&tu->p)) > return -EINTR; > > + if (atomic_inc_return(&uprobe_buffer_ref) == 1) { > + int cpu; > + > + uprobe_cpu_buffer = __alloc_percpu(PAGE_SIZE, PAGE_SIZE); > + if (uprobe_cpu_buffer == NULL) { > + atomic_dec(&uprobe_buffer_ref); > + return -ENOMEM; > + } > + > + for_each_possible_cpu(cpu) > + mutex_init(&per_cpu(uprobe_cpu_mutex, cpu)); > + } > + > WARN_ON(!uprobe_filter_is_empty(&tu->filter)); > > tu->p.flags |= flag; > @@ -646,6 +682,11 @@ static void probe_event_disable(struct trace_uprobe *tu, int flag) > if (!trace_probe_is_enabled(&tu->p)) > return; > > + if (atomic_dec_and_test(&uprobe_buffer_ref)) { > + free_percpu(uprobe_cpu_buffer); > + uprobe_cpu_buffer = NULL; > + } > + > WARN_ON(!uprobe_filter_is_empty(&tu->filter));
Do we really need atomic_t? probe_event_enable/disable is called under event_mutex and we rely on this fact anyway.
Otherwise this logic looks racy even with atomic_t, another thread could use the uninitialized uprobe_cpu_buffer/mutex if it registers another probe and the handler runs before we complete the initialization, no?
Oleg.
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