[PATCH v5 2/3] tracing/fprobe: Avoid kcalloc() in rcu_read_lock section

[Masami Hiramatsu (Google)]

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

fprobe_remove_node_in_module() is called under RCU read locked, but
this invokes kcalloc() if there are more than 8 fprobes installed
on the module. Sashiko warns it because kcalloc() can sleep [1].

 [1] https://sashiko.dev/#/patchset/177552432201.853249.5125045538812833325.stgit%40mhiramat.tok.corp.google.com

To fix this issue, expand the batch size to 128 and do not expand
the fprobe_addr_list, but just cancel walking on fprobe_ip_table,
update fgraph/ftrace_ops and retry the loop again.

Fixes: 0de4c70d04a4 ("tracing: fprobe: use rhltable for fprobe_ip_table")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
---
 Changes in v5:
  - Skip updating ftrace_ops when fails to allocate memory in module
    unloading.
 Changes in v4:
  - fix a build error typo in case of CONFIG_DYNAMIC_FTRACE=n.
 Changes in v3:
  - Retry inside rhltable_walk_enter/exit().
  - Rename fprobe_set_ips() to fprobe_remove_ips().
  - Rename 'retry' label to 'again'.
---
 kernel/trace/fprobe.c |   89 +++++++++++++++++++++++--------------------------
 1 file changed, 41 insertions(+), 48 deletions(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 1d9a3d2276cd..b5ce98d2ea96 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -346,11 +346,10 @@ static bool fprobe_is_ftrace(struct fprobe *fp)
 }
 
 #ifdef CONFIG_MODULES
-static void fprobe_set_ips(unsigned long *ips, unsigned int cnt, int remove,
-			   int reset)
+static void fprobe_remove_ips(unsigned long *ips, unsigned int cnt)
 {
-	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, remove, reset);
-	ftrace_set_filter_ips(&fprobe_ftrace_ops, ips, cnt, remove, reset);
+	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, 1, 0);
+	ftrace_set_filter_ips(&fprobe_ftrace_ops, ips, cnt, 1, 0);
 }
 #endif
 #else
@@ -369,10 +368,9 @@ static bool fprobe_is_ftrace(struct fprobe *fp)
 }
 
 #ifdef CONFIG_MODULES
-static void fprobe_set_ips(unsigned long *ips, unsigned int cnt, int remove,
-			   int reset)
+static void fprobe_remove_ips(unsigned long *ips, unsigned int cnt)
 {
-	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, remove, reset);
+	ftrace_set_filter_ips(&fprobe_graph_ops.ops, ips, cnt, 1, 0);
 }
 #endif
 #endif /* !CONFIG_DYNAMIC_FTRACE_WITH_ARGS && !CONFIG_DYNAMIC_FTRACE_WITH_REGS */
@@ -546,7 +544,7 @@ static void fprobe_graph_remove_ips(unsigned long *addrs, int num)
 
 #ifdef CONFIG_MODULES
 
-#define FPROBE_IPS_BATCH_INIT 8
+#define FPROBE_IPS_BATCH_INIT 128
 /* instruction pointer address list */
 struct fprobe_addr_list {
 	int index;
@@ -554,45 +552,24 @@ struct fprobe_addr_list {
 	unsigned long *addrs;
 };
 
-static int fprobe_addr_list_add(struct fprobe_addr_list *alist, unsigned long addr)
+static int fprobe_remove_node_in_module(struct module *mod, struct fprobe_hlist_node *node,
+					 struct fprobe_addr_list *alist)
 {
-	unsigned long *addrs;
-
-	/* Previously we failed to expand the list. */
-	if (alist->index == alist->size)
-		return -ENOSPC;
-
-	alist->addrs[alist->index++] = addr;
-	if (alist->index < alist->size)
+	if (!within_module(node->addr, mod))
 		return 0;
 
-	/* Expand the address list */
-	addrs = kcalloc(alist->size * 2, sizeof(*addrs), GFP_KERNEL);
-	if (!addrs)
-		return -ENOMEM;
-
-	memcpy(addrs, alist->addrs, alist->size * sizeof(*addrs));
-	alist->size *= 2;
-	kfree(alist->addrs);
-	alist->addrs = addrs;
+	if (delete_fprobe_node(node))
+		return 0;
+	/* If no address list is available, we can't track this address. */
+	if (!alist->addrs)
+		return 0;
 
+	alist->addrs[alist->index++] = node->addr;
+	if (alist->index == alist->size)
+		return -ENOSPC;
 	return 0;
 }
 
-static void fprobe_remove_node_in_module(struct module *mod, struct fprobe_hlist_node *node,
-					 struct fprobe_addr_list *alist)
-{
-	if (!within_module(node->addr, mod))
-		return;
-	if (delete_fprobe_node(node))
-		return;
-	/*
-	 * If failed to update alist, just continue to update hlist.
-	 * Therefore, at list user handler will not hit anymore.
-	 */
-	fprobe_addr_list_add(alist, node->addr);
-}
-
 /* Handle module unloading to manage fprobe_ip_table. */
 static int fprobe_module_callback(struct notifier_block *nb,
 				  unsigned long val, void *data)
@@ -601,29 +578,45 @@ static int fprobe_module_callback(struct notifier_block *nb,
 	struct fprobe_hlist_node *node;
 	struct rhashtable_iter iter;
 	struct module *mod = data;
+	bool retry;
 
 	if (val != MODULE_STATE_GOING)
 		return NOTIFY_DONE;
 
 	alist.addrs = kcalloc(alist.size, sizeof(*alist.addrs), GFP_KERNEL);
-	/* If failed to alloc memory, we can not remove ips from hash. */
-	if (!alist.addrs)
-		return NOTIFY_DONE;
+	/*
+	 * If failed to alloc memory, ftrace_ops will not be able to remove ips from
+	 * hash, but we can still remove nodes from fprobe_ip_table, so we can avoid
+	 * the potential wrong callback. So just print a warning here and try to
+	 * continue without address list.
+	 */
+	WARN_ONCE(!alist.addrs,
+		"Failed to allocate memory for fprobe_addr_list, ftrace_ops will not be updated");
 
 	mutex_lock(&fprobe_mutex);
 	rhltable_walk_enter(&fprobe_ip_table, &iter);
+again:
+	retry = false;
+	alist.index = 0;
 	do {
 		rhashtable_walk_start(&iter);
 
 		while ((node = rhashtable_walk_next(&iter)) && !IS_ERR(node))
-			fprobe_remove_node_in_module(mod, node, &alist);
+			if (fprobe_remove_node_in_module(mod, node, &alist) < 0) {
+				retry = true;
+				break;
+			}
 
 		rhashtable_walk_stop(&iter);
-	} while (node == ERR_PTR(-EAGAIN));
-	rhashtable_walk_exit(&iter);
+	} while (node == ERR_PTR(-EAGAIN) && !retry);
+	/* Remove any ips from hash table(s) */
+	if (alist.index > 0) {
+		fprobe_remove_ips(alist.addrs, alist.index);
+		if (retry)
+			goto again;
+	}
 
-	if (alist.index > 0)
-		fprobe_set_ips(alist.addrs, alist.index, 1, 0);
+	rhashtable_walk_exit(&iter);
 	mutex_unlock(&fprobe_mutex);
 
 	kfree(alist.addrs);