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

Peter Zijlstra
2024-07-04T08:45:35Z

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)
{
}
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,