perf/uprobe: split uprobe_unregister()

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.

We also need to add uprobe_unregister_sync() into uprobe_register()'s
error handling path, as we need to be careful about returning to the
caller before we have a guarantee that partially attached consumer won't
be called anymore. This is an unlikely slow path and this should be
totally fine to be slow in the case of a failed attach.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/20240903174603.3554182-6-andrii@kernel.org

1 files changed, 15 insertions, 6 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index e15c0306e535..694f6790e848 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1105,11 +1105,11 @@ 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;
 
@@ -1121,12 +1121,15 @@ void uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
 	/* TODO : cant unregister? schedule a worker thread */
 	if (unlikely(err)) {
 		uprobe_warn(current, "unregister, leaking uprobe");
-		goto out_sync;
+		return;
 	}
 
 	put_uprobe(uprobe);
+}
+EXPORT_SYMBOL_GPL(uprobe_unregister_nosync);
 
-out_sync:
+void uprobe_unregister_sync(void)
+{
 	/*
 	 * Now that handler_chain() and handle_uretprobe_chain() iterate over
 	 * uprobe->consumers list under RCU protection without holding
@@ -1138,7 +1141,7 @@ out_sync:
 	 */
 	synchronize_srcu(&uprobes_srcu);
 }
-EXPORT_SYMBOL_GPL(uprobe_unregister);
+EXPORT_SYMBOL_GPL(uprobe_unregister_sync);
 
 /**
  * uprobe_register - register a probe
@@ -1196,7 +1199,13 @@ 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);
 	}