Oops, sorry for confusion, this is for [9/10]. Thanks,
On Thu, 16 Jul 2026 10:59:13 +0900 Masami Hiramatsu (Google) <[email protected]> wrote: > On Wed, 15 Jul 2026 02:05:55 +0000 > [email protected] wrote: > > > Thank you for your contribution! Sashiko AI review found 8 potential > > issue(s) to consider: > > - [Critical] Deadlocks due to NMI-unsafe operations (schedule_work and > > raw_spin_lock_irqsave) in tracepoint context. > > - [High] Missing cancel_work_sync() causes a Use-After-Free of > > wprobe_trigger_data via the workqueue. > > - [High] Synchronous free of wprobe_data violates RCU removal ordering, > > risking concurrent use-after-free. > > - [High] Missing trace_event_try_get_ref() and imbalanced > > trace_event_put_ref() cause module refcount underflow. > > - [High] on_each_cpu is called with wait=false for an IPI that references > > wprobe_data. > > - [High] Immediate kfree() of RCU-protected trigger_data and wprobe_data on > > the error path. > > - [Medium] Permanent memory leak of wprobe trigger objects on successful > > registration. > > - [Medium] tw->addr is read and written concurrently by different triggers > > without a shared lock. > > -- > > > > Thanks for the review comments. > BTW, why this only to linux-perf-users? (Maybe I need to modify Sashiko > setting) > > > --- Patch [9]: [PATCH v7 09/10] tracing: wprobe: Add wprobe event trigger > > --- > > The format of this report is altered due to recitation restrictions. > > I am providing a free-form summary of the findings rather than inline > > quoting the patch. > > > > Commit: 4087513c82b11b98d27cfc4452df9a1a8e41ddd5 > > Author: Masami Hiramatsu (Google) <[email protected]> > > Subject: tracing: wprobe: Add wprobe event trigger > > > > This patch adds a wprobe event trigger to set and clear watch events > > dynamically, allowing watchpoints on local variables and slab objects. > > > > [Severity: Critical] > > Is it safe to call raw_spin_lock_irqsave() and schedule_work() directly > > from wprobe_trigger()? Tracepoints can execute in arbitrary contexts, > > including NMI or with scheduler locks held. Calling schedule_work() is > > unsafe in these contexts. Additionally, acquiring wprobe_data->lock here > > can cause a hard deadlock if the tracepoint interrupts > > wprobe_smp_update_func() > > while it is holding the exact same lock in IPI context. > > Hmm, good catch! > OK, use a pair of irq_work and work to call on_each_cpu() for some > interrupt context. > For NMI context, I think wprobe_trigger should check the original state > is in_nmi(). This can work for normal trace events or fprobe, but not > for kprobes, because kprobe handler itself is working inside NMI context. > Hmm, let me check how can I fix this. Until solving this problem, this > wprobe trigger may not work with kprobes. > Also, I found the lock should protect the wprobe itself, not data. > Let me move the irq_work and lock to trace_wprobe. > > Hmm, we may need to pass to original context (calculated by preempt_count) > to trigger event so that it can evaluate the original context. > (BTW, ) > > > [Severity: High] > > Does free_wprobe_trigger_data() safely handle the embedded work struct? > > When a trigger is unregistered, this function frees wprobe_data via kfree(). > > If wprobe_trigger() recently scheduled wprobe_data->work, the workqueue > > could execute wprobe_work_func() on the freed memory since there is no > > cancel_work_sync() before freeing. > > OK, so move the worker to wprobe because anyway the worker will update > the wprobe itself. > > > > > [Severity: High] > > Is an RCU grace period needed in wprobe_trigger_free()? > > wprobe_unregister_trigger() unlinks the trigger and calls > > wprobe_trigger_free(), which synchronously frees wprobe_data. Since > > tracepoints execute under RCU, could a concurrent tracepoint execution > > still be accessing wprobe_data when it gets freed? > > Indeed, let's use call_rcu(). > > > > > [Severity: High] > > Can the error path in wprobe_trigger_cmd_parse() cause a use-after-free? > > If event_trigger_register() successfully exposes the trigger to RCU > > readers but a subsequent step fails, returning an error causes the > > __free(kfree) cleanup to immediately free trigger_data and wprobe_data. > > This bypasses any RCU grace period for objects that were just briefly > > exposed to concurrent tracepoint readers. > > Ah, good catch. OK, let me call synchronize_rcu() before returning. > > > > > [Severity: High] > > Is it intentional that on_each_cpu() is called with wait=false in > > wprobe_work_func()? Because it doesn't wait, the work function completes > > immediately while IPIs are still pending on other CPUs. If the trigger > > is unregistered and freed right after, wprobe_smp_update_func() will > > access freed wprobe_data. > > Ah, indeed. I will use a combination of irq_worker and worker and use > on_each_cpu() with wait=true for safety. > > > > > [Severity: High] > > Does wprobe_trigger_cmd_parse() acquire the target event's module > > reference? The code calls trace_event_enable_disable() directly without > > first calling trace_event_try_get_ref(). However, wprobe_trigger_free() > > unconditionally calls trace_event_put_ref(), which could lead to a module > > refcount underflow. > > OK, let me fix it. > > > > > [Severity: Medium] > > Is there a memory leak on the success path of wprobe_trigger_cmd_parse()? > > The function increments the refcount via event_trigger_init(), and then > > event_trigger_register() increments it again. On success, trigger_data > > is set to NULL to bypass the cleanup macro, but the initial refcount is > > never dropped. When the trigger is later unregistered, the refcount only > > drops to 1, permanently leaking the objects. > > OK, call trace_event_put_ref directly in wprobe_trigger_cmd_parse(). > > > > > > [Severity: Medium] > > How is concurrent access to tw->addr synchronized between different > > triggers? If a user attaches multiple triggers (e.g., set_wprobe and > > clear_wprobe) targeting the same wprobe event, they allocate separate > > wprobe_data instances with independent locks. When wprobe_trigger() > > executes, they will read and write the shared tw->addr simultaneously > > without a common lock, potentially corrupting the hardware breakpoint state. > > I decided to use a lock in trace_wprobe side and use READ_ONCE/WRITE_ONCE() > which may be enough. > > Thank you, > > -- > Masami Hiramatsu (Google) <[email protected]> -- Masami Hiramatsu (Google) <[email protected]>
