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From:   Ming Lei <ming.lei@redhat.com>
To:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>, live-patching@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Ming Lei <ming.lei@redhat.com>
Subject: [PATCH V3 2/3] livepatch: free klp_patch object without holding klp_mutex
Date:   Mon,  1 Nov 2021 19:25:47 +0800
Message-Id: <20211101112548.3364086-3-ming.lei@redhat.com>
In-Reply-To: <20211101112548.3364086-1-ming.lei@redhat.com>
References: <20211101112548.3364086-1-ming.lei@redhat.com>
MIME-Version: 1.0
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Precedence: bulk

kobject_del() is called from kobject_put(), and after the klp_patch
kobject is deleted, any show()/store() are done.

Once the klp_patch object is removed from list and prepared for
releasing, no need to hold the global mutex of klp_mutex, so
move the freeing outside of klp_mutex.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 kernel/livepatch/core.c       | 30 ++++++++++++++++++------------
 kernel/livepatch/core.h       |  3 +--
 kernel/livepatch/transition.c | 23 +++++++++++++++++------
 kernel/livepatch/transition.h |  2 +-
 4 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index b967b4b0071b..9ede093d699a 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -327,7 +327,8 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
  */
-static int __klp_disable_patch(struct klp_patch *patch);
+static int __klp_disable_patch(struct klp_patch *patch,
+		struct list_head *to_free);
 
 static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 			     const char *buf, size_t count)
@@ -335,6 +336,7 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 	struct klp_patch *patch;
 	int ret;
 	bool enabled;
+	LIST_HEAD(to_free);
 
 	ret = kstrtobool(buf, &enabled);
 	if (ret)
@@ -360,13 +362,15 @@ static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
 	if (patch == klp_transition_patch)
 		klp_reverse_transition();
 	else if (!enabled)
-		ret = __klp_disable_patch(patch);
+		ret = __klp_disable_patch(patch, &to_free);
 	else
 		ret = -EINVAL;
 
 out:
 	mutex_unlock(&klp_mutex);
 
+	klp_free_patches_async(&to_free);
+
 	if (ret)
 		return ret;
 	return count;
@@ -693,20 +697,19 @@ static void klp_free_patch_work_fn(struct work_struct *work)
 	klp_free_patch_finish(patch);
 }
 
-void klp_free_patch_async(struct klp_patch *patch)
+static void klp_free_patch_async(struct klp_patch *patch)
 {
 	klp_free_patch_start(patch);
 	schedule_work(&patch->free_work);
 }
 
-void klp_free_replaced_patches_async(struct klp_patch *new_patch)
+void klp_free_patches_async(struct list_head *to_free)
 {
-	struct klp_patch *old_patch, *tmp_patch;
+	struct klp_patch *patch, *tmp_patch;
 
-	klp_for_each_patch_safe(old_patch, tmp_patch) {
-		if (old_patch == new_patch)
-			return;
-		klp_free_patch_async(old_patch);
+	list_for_each_entry_safe(patch, tmp_patch, to_free, list) {
+		list_del_init(&patch->list);
+		klp_free_patch_async(patch);
 	}
 }
 
@@ -915,7 +918,8 @@ static int klp_init_patch(struct klp_patch *patch)
 	return 0;
 }
 
-static int __klp_disable_patch(struct klp_patch *patch)
+static int __klp_disable_patch(struct klp_patch *patch,
+		struct list_head *to_free)
 {
 	struct klp_object *obj;
 
@@ -942,7 +946,7 @@ static int __klp_disable_patch(struct klp_patch *patch)
 
 	klp_start_transition();
 	patch->enabled = false;
-	klp_try_complete_transition();
+	klp_try_complete_transition(to_free);
 
 	return 0;
 }
@@ -951,6 +955,7 @@ static int __klp_enable_patch(struct klp_patch *patch)
 {
 	struct klp_object *obj;
 	int ret;
+	LIST_HEAD(unused);
 
 	if (klp_transition_patch)
 		return -EBUSY;
@@ -992,7 +997,8 @@ static int __klp_enable_patch(struct klp_patch *patch)
 
 	klp_start_transition();
 	patch->enabled = true;
-	klp_try_complete_transition();
+	klp_try_complete_transition(&unused);
+	WARN_ON_ONCE(!list_empty(&unused));
 
 	return 0;
 err:
diff --git a/kernel/livepatch/core.h b/kernel/livepatch/core.h
index 38209c7361b6..8ff97745ba40 100644
--- a/kernel/livepatch/core.h
+++ b/kernel/livepatch/core.h
@@ -13,8 +13,7 @@ extern struct list_head klp_patches;
 #define klp_for_each_patch(patch)	\
 	list_for_each_entry(patch, &klp_patches, list)
 
-void klp_free_patch_async(struct klp_patch *patch);
-void klp_free_replaced_patches_async(struct klp_patch *new_patch);
+void klp_free_patches_async(struct list_head *to_free);
 void klp_unpatch_replaced_patches(struct klp_patch *new_patch);
 void klp_discard_nops(struct klp_patch *new_patch);
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 291b857a6e20..a9ebc9c5db02 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -32,12 +32,16 @@ static unsigned int klp_signals_cnt;
  */
 static void klp_transition_work_fn(struct work_struct *work)
 {
+	LIST_HEAD(to_free);
+
 	mutex_lock(&klp_mutex);
 
 	if (klp_transition_patch)
-		klp_try_complete_transition();
+		klp_try_complete_transition(&to_free);
 
 	mutex_unlock(&klp_mutex);
+
+	klp_free_patches_async(&to_free);
 }
 static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
 
@@ -384,7 +388,7 @@ static void klp_send_signals(void)
  *
  * If any tasks are still stuck in the initial patch state, schedule a retry.
  */
-void klp_try_complete_transition(void)
+void klp_try_complete_transition(struct list_head *to_free)
 {
 	unsigned int cpu;
 	struct task_struct *g, *task;
@@ -449,10 +453,17 @@ void klp_try_complete_transition(void)
 	 * klp_complete_transition() but it is called also
 	 * from klp_cancel_transition().
 	 */
-	if (!patch->enabled)
-		klp_free_patch_async(patch);
-	else if (patch->replace)
-		klp_free_replaced_patches_async(patch);
+	if (!patch->enabled) {
+		list_move(&patch->list, to_free);
+	} else if (patch->replace) {
+		struct klp_patch *old_patch, *tmp_patch;
+
+		klp_for_each_patch_safe(old_patch, tmp_patch) {
+			if (old_patch == patch)
+				break;
+			list_move(&old_patch->list, to_free);
+		}
+	}
 }
 
 /*
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
index 322db16233de..20e3a5a0cbce 100644
--- a/kernel/livepatch/transition.h
+++ b/kernel/livepatch/transition.h
@@ -9,7 +9,7 @@ extern struct klp_patch *klp_transition_patch;
 void klp_init_transition(struct klp_patch *patch, int state);
 void klp_cancel_transition(void);
 void klp_start_transition(void);
-void klp_try_complete_transition(void);
+void klp_try_complete_transition(struct list_head *to_free);
 void klp_reverse_transition(void);
 void klp_force_transition(void);
 
-- 
2.31.1