Re: [PATCH 6/8] perf/uprobe: split uprobe_unregister()

Liao, Chang
2024-08-02T02:41:20Z

在 2024/8/1 5:42, Andrii Nakryiko 写道:
> From: Peter Zijlstra <peterz@infradead.org>
>
> With uprobe_unregister() having grown a synchronize_srcu(), it becomes
> fairly slow to call. Esp. since both users of this API call it in a
> loop.
>
> Peel off the sync_srcu() and do it once, after the loop.
>
> With recent uprobe_register()'s error handling reusing full
> uprobe_unregister() call, we need to be careful about returning to the
> caller before we have a guarantee that partially attached consumer won't
> be called anymore. So add uprobe_unregister_sync() in the error handling
> path. This is an unlikely slow path and this should be totally fine to
> be slow in the case of an failed attach.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Co-developed-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
> include/linux/uprobes.h | 8 ++++++--
> kernel/events/uprobes.c | 18 ++++++++++++++----
> kernel/trace/bpf_trace.c | 5 ++++-
> kernel/trace/trace_uprobe.c | 6 +++++-
> .../selftests/bpf/bpf_testmod/bpf_testmod.c | 3 ++-
> 5 files changed, 31 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index a1686c1ebcb6..8f1999eb9d9f 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -105,7 +105,8 @@ extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_t);
> extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
> extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
> -extern void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc);
> +extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
> +extern void uprobe_unregister_sync(void);

[...]

> static inline void
> -uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
> +uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc)
> +{
> +}
> +static inline void uprobes_unregister_sync(void)

*uprobes*_unregister_sync, is it a typo?

> {
> }
> static inline int uprobe_mmap(struct vm_area_struct *vma)
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 3b42fd355256..b0488d356399 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1089,11 +1089,11 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
> }
>
> /**
> - * uprobe_unregister - unregister an already registered probe.
> + * uprobe_unregister_nosync - unregister an already registered probe.
> * @uprobe: uprobe to remove
> * @uc: identify which probe if multiple probes are colocated.
> */
> -void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
> +void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc)
> {
> int err;
>
> @@ -1109,10 +1109,14 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
> return;
>
> put_uprobe(uprobe);
> +}
> +EXPORT_SYMBOL_GPL(uprobe_unregister_nosync);
>
> +void uprobe_unregister_sync(void)
> +{
> synchronize_srcu(&uprobes_srcu);
> }
> -EXPORT_SYMBOL_GPL(uprobe_unregister);
> +EXPORT_SYMBOL_GPL(uprobe_unregister_sync);
>
> /**
> * uprobe_register - register a probe
> @@ -1170,7 +1174,13 @@ struct uprobe *uprobe_register(struct inode *inode,
> up_write(&uprobe->register_rwsem);
>
> if (ret) {
> - uprobe_unregister(uprobe, uc);
> + uprobe_unregister_nosync(uprobe, uc);
> + /*
> + * Registration might have partially succeeded, so we can have
> + * this consumer being called right at this time. We need to
> + * sync here. It's ok, it's unlikely slow path.
> + */
> + uprobe_unregister_sync();
> return ERR_PTR(ret);
> }
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 73c570b5988b..6b632710c98e 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3184,7 +3184,10 @@ static void bpf_uprobe_unregister(struct bpf_uprobe *uprobes, u32 cnt)
> u32 i;
>
> for (i = 0; i < cnt; i++)
> - uprobe_unregister(uprobes[i].uprobe, &uprobes[i].consumer);
> + uprobe_unregister_nosync(uprobes[i].uprobe, &uprobes[i].consumer);
> +
> + if (cnt)
> + uprobe_unregister_sync();
> }
>
> static void bpf_uprobe_multi_link_release(struct bpf_link *link)
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 7eb79e0a5352..f7443e996b1b 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -1097,6 +1097,7 @@ static int trace_uprobe_enable(struct trace_uprobe *tu, filter_func_t filter)
> static void __probe_event_disable(struct trace_probe *tp)
> {
> struct trace_uprobe *tu;
> + bool sync = false;
>
> tu = container_of(tp, struct trace_uprobe, tp);
> WARN_ON(!uprobe_filter_is_empty(tu->tp.event->filter));
> @@ -1105,9 +1106,12 @@ static void __probe_event_disable(struct trace_probe *tp)
> if (!tu->uprobe)
> continue;
>
> - uprobe_unregister(tu->uprobe, &tu->consumer);
> + uprobe_unregister_nosync(tu->uprobe, &tu->consumer);
> + sync = true;
> tu->uprobe = NULL;
> }
> + if (sync)
> + uprobe_unregister_sync();
> }
>
> static int probe_event_enable(struct trace_event_call *call,
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 73a6b041bcce..928c73cde32e 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -478,7 +478,8 @@ static void testmod_unregister_uprobe(void)
> mutex_lock(&testmod_uprobe_mutex);
>
> if (uprobe.uprobe) {
> - uprobe_unregister(uprobe.uprobe, &uprobe.consumer);
> + uprobe_unregister_nosync(uprobe.uprobe, &uprobe.consumer);
> + uprobe_unregister_sync();
> uprobe.offset = 0;
> uprobe.uprobe = NULL;
> }

--
BR
Liao, Chang