[PATCH v7 2/6] tracing/fprobe: Unregister fprobe even if memory allocation fails

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

unregister_fprobe() can fail under memory pressure because of memory
allocation failure, but this maybe called from module unloading, and
usually there is no way to retry it. Moreover. trace_fprobe does not
check the return value.

To fix this problem, unregister fprobe and fprobe_hash_node even if
working memory allocation fails.
Anyway, if the last fprobe is removed, the filter will be freed.

Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 Changes in v7:
  - Newly added.
---
 kernel/trace/fprobe.c |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index fc7018b28fdd..d634eb8e8b9e 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -934,15 +934,19 @@ int unregister_fprobe(struct fprobe *fp)
 
 	hlist_array = fp->hlist_array;
 	addrs = kcalloc(hlist_array->size, sizeof(unsigned long), GFP_KERNEL);
-	if (!addrs) {
-		ret = -ENOMEM;	/* TODO: Fallback to one-by-one loop */
-		goto out;
-	}
+	/*
+	 * This will remove fprobe_hash_node from the hash table even if
+	 * memory allocation fails. However, ftrace_ops will not be updated.
+	 * Anyway, when the last fprobe is unregistered, ftrace_ops is also
+	 * unregistered.
+	 */
+	if (!addrs)
+		pr_warn("Failed to allocate working array. ftrace_ops may not sync.\n");
 
 	/* Remove non-synonim ips from table and hash */
 	count = 0;
 	for (i = 0; i < hlist_array->size; i++) {
-		if (!delete_fprobe_node(&hlist_array->array[i]))
+		if (!delete_fprobe_node(&hlist_array->array[i]) && addrs)
 			addrs[count++] = hlist_array->array[i].addr;
 	}
 	del_fprobe_hash(fp);