Re: [PATCH v2 04/12] uprobes: revamp uprobe refcounting and lifetime management

Masami Hiramatsu
2024-07-04T14:40:07Z

On Thu, 4 Jul 2024 10:45:24 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Jul 04, 2024 at 10:03:48AM +0200, Peter Zijlstra wrote:
>
> > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> > index c98e3b3386ba..4aafb4485be7 100644
> > --- a/kernel/trace/trace_uprobe.c
> > +++ b/kernel/trace/trace_uprobe.c
> > @@ -1112,7 +1112,8 @@ static void __probe_event_disable(struct trace_probe *tp)
> > if (!tu->inode)
> > continue;
> >
> > - uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> > + uprobe_unregister(tu->inode, tu->offset, &tu->consumer,
> > + list_is_last(trace_probe_probe_list(tp), &tu->tp.list) ? 0 : URF_NO_SYNC);
> > tu->inode = NULL;
> > }
> > }
>
>
> Hmm, that continue clause might ruin things. Still easy enough to add
> uprobe_unregister_sync() and simpy always pass URF_NO_SYNC.
>
> I really don't see why we should make this more complicated than it
> needs to be.
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 354cab634341..681741a51df3 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -115,7 +115,9 @@ extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm
> extern int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
> extern int uprobe_register_refctr(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
> extern int uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, bool);
> -extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc);
> +#define URF_NO_SYNC 0x01
> +extern void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, unsigned int flags);
> +extern void uprobe_unregister_sync(void);
> extern int uprobe_mmap(struct vm_area_struct *vma);
> extern void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end);
> extern void uprobe_start_dup_mmap(void);
> @@ -165,7 +167,7 @@ uprobe_apply(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, boo
> return -ENOSYS;
> }
> static inline void
> -uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
> +uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, unsigned int flags)

nit: IMHO, I would like to see uprobe_unregister_nosync() variant instead of
adding flags.

Thank you,

> {
> }
> static inline int uprobe_mmap(struct vm_area_struct *vma)
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 0b7574a54093..d09f7b942076 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1145,7 +1145,7 @@ __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
> * @offset: offset from the start of the file.
> * @uc: identify which probe if multiple probes are colocated.
> */
> -void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
> +void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc, unsigned int flags)
> {
> scoped_guard (srcu, &uprobe_srcu) {
> struct uprobe *uprobe = find_uprobe(inode, offset);
> @@ -1157,10 +1157,17 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume
> mutex_unlock(&uprobe->register_mutex);
> }
>
> - synchronize_srcu(&uprobe_srcu); // XXX amortize / batch
> + if (!(flags & URF_NO_SYNC))
> + synchronize_srcu(&uprobe_srcu);
> }
> EXPORT_SYMBOL_GPL(uprobe_unregister);
>
> +void uprobe_unregister_sync(void)
> +{
> + synchronize_srcu(&uprobe_srcu);
> +}
> +EXPORT_SYMBOL_GPL(uprobe_unregister_sync);
> +
> /*
> * __uprobe_register - register a probe
> * @inode: the file in which the probe has to be placed.
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index d1daeab1bbc1..1f6adabbb1e7 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3181,9 +3181,10 @@ static void bpf_uprobe_unregister(struct path *path, struct bpf_uprobe *uprobes,
> u32 i;
>
> for (i = 0; i < cnt; i++) {
> - uprobe_unregister(d_real_inode(path->dentry), uprobes[i].offset,
> - &uprobes[i].consumer);
> + uprobe_unregister(d_real_inode(path->dentry), uprobes[i].offset, URF_NO_SYNC);
> }
> + if (cnt > 0)
> + 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 c98e3b3386ba..6b64470a1c5c 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -1104,6 +1104,7 @@ 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));
> @@ -1112,9 +1113,12 @@ static void __probe_event_disable(struct trace_probe *tp)
> if (!tu->inode)
> continue;
>
> - uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> + uprobe_unregister(tu->inode, tu->offset, &tu->consumer, URF_NO_SYNC);
> + sync = true;
> tu->inode = NULL;
> }
> + if (sync)
> + uprobe_unregister_sync();
> }
>
> static int probe_event_enable(struct trace_event_call *call,

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>