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

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jul 03, 2024 at 01:47:23PM -0700, Andrii Nakryiko wrote:
> Your innocuous "// XXX amortize / batch" comment below is *the major
> point of this patch set*. Try to appreciate that. It's not a small
> todo, it took this entire patch set to allow for that.

Tada!

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 354cab634341..c9c9ec87ab9a 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -115,7 +115,8 @@ 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 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 +166,7 @@ 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..1f4151c518ed 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);
@@ -1157,7 +1157,8 @@ 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);
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d1daeab1bbc1..950b5241244a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3182,7 +3182,7 @@ static void bpf_uprobe_unregister(struct path *path, struct bpf_uprobe *uprobes,
 
 	for (i = 0; i < cnt; i++) {
 		uprobe_unregister(d_real_inode(path->dentry), uprobes[i].offset,
-				  &uprobes[i].consumer);
+				  &uprobes[i].consumer, i != cnt-1 ? URF_NO_SYNC : 0);
 	}
 }
 
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;
 	}
 }