linux-kernel - [RFT PATCH 07/13] kprobes: Use normal list traversal API if a mutex is held

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Message-Id: <157918592332.29301.1564446199611592837.stgit@devnote2>
Date:   Thu, 16 Jan 2020 23:45:23 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Brendan Gregg <brendan.d.gregg@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     mhiramat@...nel.org, Ingo Molnar <mingo@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "David S . Miller" <davem@...emloft.net>, paulmck@...nel.org,
        joel@...lfernandes.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Subject: [RFT PATCH 07/13] kprobes: Use normal list traversal API if a mutex is held

Use normal list traversal API instead of rcu_read_lock,
RCU list traversal and rcu_read_unlock pair if a mutex
which protects the list is held in the methods of
kprobe_insn_cache.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/kprobes.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 848c14e92ccc..09b0e33bc845 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -141,8 +141,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 	/* Since the slot array is not protected by rcu, we need a mutex */
 	mutex_lock(&c->mutex);
  retry:
-	rcu_read_lock();
-	list_for_each_entry_rcu(kip, &c->pages, list) {
+	list_for_each_entry(kip, &c->pages, list) {
 		if (kip->nused < slots_per_page(c)) {
 			int i;
 			for (i = 0; i < slots_per_page(c); i++) {
@@ -150,7 +149,6 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 					kip->slot_used[i] = SLOT_USED;
 					kip->nused++;
 					slot = kip->insns + (i * c->insn_size);
-					rcu_read_unlock();
 					goto out;
 				}
 			}
@@ -159,7 +157,6 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c)
 			WARN_ON(1);
 		}
 	}
-	rcu_read_unlock();
 
 	/* If there are any garbage slots, collect it and try again. */
 	if (c->nr_garbage && collect_garbage_slots(c) == 0)
@@ -244,8 +241,7 @@ void __free_insn_slot(struct kprobe_insn_cache *c,
 	long idx;
 
 	mutex_lock(&c->mutex);
-	rcu_read_lock();
-	list_for_each_entry_rcu(kip, &c->pages, list) {
+	list_for_each_entry(kip, &c->pages, list) {
 		idx = ((long)slot - (long)kip->insns) /
 			(c->insn_size * sizeof(kprobe_opcode_t));
 		if (idx >= 0 && idx < slots_per_page(c))
@@ -255,7 +251,6 @@ void __free_insn_slot(struct kprobe_insn_cache *c,
 	WARN_ON(1);
 	kip = NULL;
 out:
-	rcu_read_unlock();
 	/* Mark and sweep: this may sleep */
 	if (kip) {
 		/* Check double free */