[PATCH v1 0/3] Binder: Enable App Freezing Capability

[PATCH v1 0/3] Binder: Enable App Freezing Capability

[Li Li]

From: Li Li <dualli@google.com>

To improve the user experience when switching between recently used
applications, the background applications which are not currently needed
are cached in the memory. Normally, a well designed application will not
consume valuable CPU resources in the background. However, it's possible
some applications are not able or willing to behave as expected, wasting
energy even after being cached.

It is a good idea to freeze those applications when they're only being
kept alive for the sake of faster startup and energy saving. These kernel
patches will provide the necessary infrastructure for user space framework
to freeze and thaw a cached process, check the current freezing status and
correctly deal with outstanding binder transactions to frozen processes.

Marco Ballesio (3):
  binder: BINDER_FREEZE ioctl
  binder: use EINTR for interrupted wait for work
  binder: BINDER_GET_FROZEN_INFO ioctl

 drivers/android/binder.c            | 196 ++++++++++++++++++++++++++--
 drivers/android/binder_internal.h   |  18 +++
 include/uapi/linux/android/binder.h |  20 +++
 3 files changed, 222 insertions(+), 12 deletions(-)

-- 
2.31.0.rc1.246.gcd05c9c855-goog

[PATCH v1 1/3] binder: BINDER_FREEZE ioctl

[Li Li]

From: Marco Ballesio <balejs@google.com>

Frozen tasks can't process binder transactions, so a way is required to
inform transmitting ends of communication failures due to the frozen
state of their receiving counterparts. Additionally, races are possible
between transitions to frozen state and binder transactions enqueued to
a specific process.

Implement BINDER_FREEZE ioctl for user space to inform the binder driver
about the intention to freeze or unfreeze a process. When the ioctl is
called, block the caller until any pending binder transactions toward
the target process are flushed. Return an error to transactions to
processes marked as frozen.

Signed-off-by: Marco Ballesio <balejs@google.com>
Co-developed-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Li Li <dualli@google.com>
---
 drivers/android/binder.c            | 137 ++++++++++++++++++++++++++--
 drivers/android/binder_internal.h   |  12 +++
 include/uapi/linux/android/binder.h |  13 +++
 3 files changed, 152 insertions(+), 10 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index c119736ca56a..9ec3ba038652 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1506,6 +1506,10 @@ static void binder_free_transaction(struct binder_transaction *t)
 
 	if (target_proc) {
 		binder_inner_proc_lock(target_proc);
+		target_proc->outstanding_txns--;
+		WARN_ON(target_proc->outstanding_txns < 0);
+		if (!target_proc->outstanding_txns && target_proc->is_frozen)
+			wake_up_interruptible_all(&target_proc->freeze_wait);
 		if (t->buffer)
 			t->buffer->transaction = NULL;
 		binder_inner_proc_unlock(target_proc);
@@ -2331,10 +2335,11 @@ static int binder_fixup_parent(struct binder_transaction *t,
  * If the @thread parameter is not NULL, the transaction is always queued
  * to the waitlist of that specific thread.
  *
- * Return:	true if the transactions was successfully queued
- *		false if the target process or thread is dead
+ * Return:	0 if the transaction was successfully queued
+ *		BR_DEAD_REPLY if the target process or thread is dead
+ *		BR_FROZEN_REPLY if the target process or thread is frozen
  */
-static bool binder_proc_transaction(struct binder_transaction *t,
+static int binder_proc_transaction(struct binder_transaction *t,
 				    struct binder_proc *proc,
 				    struct binder_thread *thread)
 {
@@ -2354,10 +2359,13 @@ static bool binder_proc_transaction(struct binder_transaction *t,
 
 	binder_inner_proc_lock(proc);
 
-	if (proc->is_dead || (thread && thread->is_dead)) {
+	if ((proc->is_frozen && !oneway) || proc->is_dead ||
+			(thread && thread->is_dead)) {
+		bool proc_is_dead = proc->is_dead
+			|| (thread && thread->is_dead);
 		binder_inner_proc_unlock(proc);
 		binder_node_unlock(node);
-		return false;
+		return proc_is_dead ? BR_DEAD_REPLY : BR_FROZEN_REPLY;
 	}
 
 	if (!thread && !pending_async)
@@ -2373,10 +2381,11 @@ static bool binder_proc_transaction(struct binder_transaction *t,
 	if (!pending_async)
 		binder_wakeup_thread_ilocked(proc, thread, !oneway /* sync */);
 
+	proc->outstanding_txns++;
 	binder_inner_proc_unlock(proc);
 	binder_node_unlock(node);
 
-	return true;
+	return 0;
 }
 
 /**
@@ -3013,13 +3022,16 @@ static void binder_transaction(struct binder_proc *proc,
 	if (reply) {
 		binder_enqueue_thread_work(thread, tcomplete);
 		binder_inner_proc_lock(target_proc);
-		if (target_thread->is_dead) {
+		if (target_thread->is_dead || target_proc->is_frozen) {
+			return_error = target_thread->is_dead ?
+				BR_DEAD_REPLY : BR_FROZEN_REPLY;
 			binder_inner_proc_unlock(target_proc);
 			goto err_dead_proc_or_thread;
 		}
 		BUG_ON(t->buffer->async_transaction != 0);
 		binder_pop_transaction_ilocked(target_thread, in_reply_to);
 		binder_enqueue_thread_work_ilocked(target_thread, &t->work);
+		target_proc->outstanding_txns++;
 		binder_inner_proc_unlock(target_proc);
 		wake_up_interruptible_sync(&target_thread->wait);
 		binder_free_transaction(in_reply_to);
@@ -3038,7 +3050,9 @@ static void binder_transaction(struct binder_proc *proc,
 		t->from_parent = thread->transaction_stack;
 		thread->transaction_stack = t;
 		binder_inner_proc_unlock(proc);
-		if (!binder_proc_transaction(t, target_proc, target_thread)) {
+		return_error = binder_proc_transaction(t,
+				target_proc, target_thread);
+		if (return_error) {
 			binder_inner_proc_lock(proc);
 			binder_pop_transaction_ilocked(thread, t);
 			binder_inner_proc_unlock(proc);
@@ -3048,7 +3062,8 @@ static void binder_transaction(struct binder_proc *proc,
 		BUG_ON(target_node == NULL);
 		BUG_ON(t->buffer->async_transaction != 1);
 		binder_enqueue_thread_work(thread, tcomplete);
-		if (!binder_proc_transaction(t, target_proc, NULL))
+		return_error = binder_proc_transaction(t, target_proc, NULL);
+		if (return_error)
 			goto err_dead_proc_or_thread;
 	}
 	if (target_thread)
@@ -3065,7 +3080,6 @@ static void binder_transaction(struct binder_proc *proc,
 	return;
 
 err_dead_proc_or_thread:
-	return_error = BR_DEAD_REPLY;
 	return_error_line = __LINE__;
 	binder_dequeue_work(proc, tcomplete);
 err_translate_failed:
@@ -4298,6 +4312,7 @@ static void binder_free_proc(struct binder_proc *proc)
 
 	BUG_ON(!list_empty(&proc->todo));
 	BUG_ON(!list_empty(&proc->delivered_death));
+	WARN_ON(proc->outstanding_txns);
 	device = container_of(proc->context, struct binder_device, context);
 	if (refcount_dec_and_test(&device->ref)) {
 		kfree(proc->context->name);
@@ -4359,6 +4374,7 @@ static int binder_thread_release(struct binder_proc *proc,
 			     (t->to_thread == thread) ? "in" : "out");
 
 		if (t->to_thread == thread) {
+			thread->proc->outstanding_txns--;
 			t->to_proc = NULL;
 			t->to_thread = NULL;
 			if (t->buffer) {
@@ -4609,6 +4625,45 @@ static int binder_ioctl_get_node_debug_info(struct binder_proc *proc,
 	return 0;
 }
 
+static int binder_ioctl_freeze(struct binder_freeze_info *info,
+			       struct binder_proc *target_proc)
+{
+	int ret = 0;
+
+	if (!info->enable) {
+		binder_inner_proc_lock(target_proc);
+		target_proc->is_frozen = false;
+		binder_inner_proc_unlock(target_proc);
+		return 0;
+	}
+
+	/*
+	 * Freezing the target. Prevent new transactions by
+	 * setting frozen state. If timeout specified, wait
+	 * for transactions to drain.
+	 */
+	binder_inner_proc_lock(target_proc);
+	target_proc->is_frozen = true;
+	binder_inner_proc_unlock(target_proc);
+
+	if (info->timeout_ms > 0)
+		ret = wait_event_interruptible_timeout(
+			target_proc->freeze_wait,
+			(!target_proc->outstanding_txns),
+			msecs_to_jiffies(info->timeout_ms));
+
+	if (!ret && target_proc->outstanding_txns)
+		ret = -EAGAIN;
+
+	if (ret < 0) {
+		binder_inner_proc_lock(target_proc);
+		target_proc->is_frozen = false;
+		binder_inner_proc_unlock(target_proc);
+	}
+
+	return ret;
+}
+
 static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int ret;
@@ -4727,6 +4782,66 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		}
 		break;
 	}
+	case BINDER_FREEZE: {
+		struct binder_freeze_info info;
+		struct binder_proc **target_procs = NULL, *target_proc;
+		int target_procs_count = 0, i = 0;
+
+		ret = 0;
+
+		if (copy_from_user(&info, ubuf, sizeof(info))) {
+			ret = -EFAULT;
+			goto err;
+		}
+
+		mutex_lock(&binder_procs_lock);
+		hlist_for_each_entry(target_proc, &binder_procs, proc_node) {
+			if (target_proc->pid == info.pid)
+				target_procs_count++;
+		}
+
+		if (target_procs_count == 0) {
+			mutex_unlock(&binder_procs_lock);
+			ret = -EINVAL;
+			goto err;
+		}
+
+		target_procs = kcalloc(target_procs_count,
+				       sizeof(struct binder_proc *),
+				       GFP_KERNEL);
+
+		if (!target_procs) {
+			mutex_unlock(&binder_procs_lock);
+			ret = -ENOMEM;
+			goto err;
+		}
+
+		hlist_for_each_entry(target_proc, &binder_procs, proc_node) {
+			if (target_proc->pid != info.pid)
+				continue;
+
+			binder_inner_proc_lock(target_proc);
+			target_proc->tmp_ref++;
+			binder_inner_proc_unlock(target_proc);
+
+			target_procs[i++] = target_proc;
+		}
+		mutex_unlock(&binder_procs_lock);
+
+		for (i = 0; i < target_procs_count; i++) {
+			if (ret >= 0)
+				ret = binder_ioctl_freeze(&info,
+							  target_procs[i]);
+
+			binder_proc_dec_tmpref(target_procs[i]);
+		}
+
+		kfree(target_procs);
+
+		if (ret < 0)
+			goto err;
+		break;
+	}
 	default:
 		ret = -EINVAL;
 		goto err;
@@ -4823,6 +4938,7 @@ static int binder_open(struct inode *nodp, struct file *filp)
 	get_task_struct(current->group_leader);
 	proc->tsk = current->group_leader;
 	INIT_LIST_HEAD(&proc->todo);
+	init_waitqueue_head(&proc->freeze_wait);
 	proc->default_priority = task_nice(current);
 	/* binderfs stashes devices in i_private */
 	if (is_binderfs_device(nodp)) {
@@ -5035,6 +5151,7 @@ static void binder_deferred_release(struct binder_proc *proc)
 	proc->tmp_ref++;
 
 	proc->is_dead = true;
+	proc->is_frozen = false;
 	threads = 0;
 	active_transactions = 0;
 	while ((n = rb_first(&proc->threads))) {
diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
index 6cd79011e35d..e6a53e98c6da 100644
--- a/drivers/android/binder_internal.h
+++ b/drivers/android/binder_internal.h
@@ -367,9 +367,18 @@ struct binder_ref {
  *                        (protected by binder_deferred_lock)
  * @deferred_work:        bitmap of deferred work to perform
  *                        (protected by binder_deferred_lock)
+ * @outstanding_txns:     number of transactions to be transmitted before
+ *                        processes in freeze_wait are woken up
+ *                        (protected by @inner_lock)
  * @is_dead:              process is dead and awaiting free
  *                        when outstanding transactions are cleaned up
  *                        (protected by @inner_lock)
+ * @is_frozen:            process is frozen and unable to service
+ *                        binder transactions
+ *                        (protected by @inner_lock)
+ * @freeze_wait:          waitqueue of processes waiting for all outstanding
+ *                        transactions to be processed
+ *                        (protected by @inner_lock)
  * @todo:                 list of work for this process
  *                        (protected by @inner_lock)
  * @stats:                per-process binder statistics
@@ -410,7 +419,10 @@ struct binder_proc {
 	struct task_struct *tsk;
 	struct hlist_node deferred_work_node;
 	int deferred_work;
+	int outstanding_txns;
 	bool is_dead;
+	bool is_frozen;
+	wait_queue_head_t freeze_wait;
 
 	struct list_head todo;
 	struct binder_stats stats;
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index ec84ad106568..7eb5b818b3c1 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -217,6 +217,12 @@ struct binder_node_info_for_ref {
 	__u32            reserved3;
 };
 
+struct binder_freeze_info {
+	__u32            pid;
+	__u32            enable;
+	__u32            timeout_ms;
+};
+
 #define BINDER_WRITE_READ		_IOWR('b', 1, struct binder_write_read)
 #define BINDER_SET_IDLE_TIMEOUT		_IOW('b', 3, __s64)
 #define BINDER_SET_MAX_THREADS		_IOW('b', 5, __u32)
@@ -227,6 +233,7 @@ struct binder_node_info_for_ref {
 #define BINDER_GET_NODE_DEBUG_INFO	_IOWR('b', 11, struct binder_node_debug_info)
 #define BINDER_GET_NODE_INFO_FOR_REF	_IOWR('b', 12, struct binder_node_info_for_ref)
 #define BINDER_SET_CONTEXT_MGR_EXT	_IOW('b', 13, struct flat_binder_object)
+#define BINDER_FREEZE			_IOW('b', 14, struct binder_freeze_info)
 
 /*
  * NOTE: Two special error codes you should check for when calling
@@ -408,6 +415,12 @@ enum binder_driver_return_protocol {
 	 * The last transaction (either a bcTRANSACTION or
 	 * a bcATTEMPT_ACQUIRE) failed (e.g. out of memory).  No parameters.
 	 */
+
+	BR_FROZEN_REPLY = _IO('r', 18),
+	/*
+	 * The target of the last transaction (either a bcTRANSACTION or
+	 * a bcATTEMPT_ACQUIRE) is frozen.  No parameters.
+	 */
 };
 
 enum binder_driver_command_protocol {
-- 
2.31.0.rc1.246.gcd05c9c855-goog

[PATCH v1 2/3] binder: use EINTR for interrupted wait for work

[Li Li]

From: Marco Ballesio <balejs@google.com>

when interrupted by a signal, binder_wait_for_work currently returns
-ERESTARTSYS. This error code isn't propagated to user space, but a way
to handle interruption due to signals must be provided to code using
this API.

Replace this instance of -ERESTARTSYS with -EINTR, which is propagated
to user space.

Test: built, booted, interrupted a worker thread within
binder_wait_for_work
Signed-off-by: Marco Ballesio <balejs@google.com>
Signed-off-by: Li Li <dualli@google.com>
---
 drivers/android/binder.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 9ec3ba038652..34c3e430a270 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3710,7 +3710,7 @@ static int binder_wait_for_work(struct binder_thread *thread,
 		binder_inner_proc_lock(proc);
 		list_del_init(&thread->waiting_thread_node);
 		if (signal_pending(current)) {
-			ret = -ERESTARTSYS;
+			ret = -EINTR;
 			break;
 		}
 	}
@@ -4851,7 +4851,7 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 	if (thread)
 		thread->looper_need_return = false;
 	wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
-	if (ret && ret != -ERESTARTSYS)
+	if (ret && ret != -EINTR)
 		pr_info("%d:%d ioctl %x %lx returned %d\n", proc->pid, current->pid, cmd, arg, ret);
 err_unlocked:
 	trace_binder_ioctl_done(ret);
-- 
2.31.0.rc1.246.gcd05c9c855-goog

[PATCH v1 3/3] binder: BINDER_GET_FROZEN_INFO ioctl

[Li Li]

From: Marco Ballesio <balejs@google.com>

User space needs to know if binder transactions occurred to frozen
processes. Introduce a new BINDER_GET_FROZEN ioctl and keep track of
transactions occurring to frozen proceses.

Signed-off-by: Marco Ballesio <balejs@google.com>
Signed-off-by: Li Li <dualli@google.com>
---
 drivers/android/binder.c            | 55 +++++++++++++++++++++++++++++
 drivers/android/binder_internal.h   |  6 ++++
 include/uapi/linux/android/binder.h |  7 ++++
 3 files changed, 68 insertions(+)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 34c3e430a270..00c68b7eb553 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2358,6 +2358,10 @@ static int binder_proc_transaction(struct binder_transaction *t,
 	}
 
 	binder_inner_proc_lock(proc);
+	if (proc->is_frozen) {
+		proc->sync_recv |= !oneway;
+		proc->async_recv |= oneway;
+	}
 
 	if ((proc->is_frozen && !oneway) || proc->is_dead ||
 			(thread && thread->is_dead)) {
@@ -4632,6 +4636,8 @@ static int binder_ioctl_freeze(struct binder_freeze_info *info,
 
 	if (!info->enable) {
 		binder_inner_proc_lock(target_proc);
+		target_proc->sync_recv = false;
+		target_proc->async_recv = false;
 		target_proc->is_frozen = false;
 		binder_inner_proc_unlock(target_proc);
 		return 0;
@@ -4643,6 +4649,8 @@ static int binder_ioctl_freeze(struct binder_freeze_info *info,
 	 * for transactions to drain.
 	 */
 	binder_inner_proc_lock(target_proc);
+	target_proc->sync_recv = false;
+	target_proc->async_recv = false;
 	target_proc->is_frozen = true;
 	binder_inner_proc_unlock(target_proc);
 
@@ -4664,6 +4672,33 @@ static int binder_ioctl_freeze(struct binder_freeze_info *info,
 	return ret;
 }
 
+static int binder_ioctl_get_freezer_info(
+				struct binder_frozen_status_info *info)
+{
+	struct binder_proc *target_proc;
+	bool found = false;
+
+	info->sync_recv = 0;
+	info->async_recv = 0;
+
+	mutex_lock(&binder_procs_lock);
+	hlist_for_each_entry(target_proc, &binder_procs, proc_node) {
+		if (target_proc->pid == info->pid) {
+			found = true;
+			binder_inner_proc_lock(target_proc);
+			info->sync_recv |= target_proc->sync_recv;
+			info->async_recv |= target_proc->async_recv;
+			binder_inner_proc_unlock(target_proc);
+		}
+	}
+	mutex_unlock(&binder_procs_lock);
+
+	if (!found)
+		return -EINVAL;
+
+	return 0;
+}
+
 static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int ret;
@@ -4842,6 +4877,24 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 			goto err;
 		break;
 	}
+	case BINDER_GET_FROZEN_INFO: {
+		struct binder_frozen_status_info info;
+
+		if (copy_from_user(&info, ubuf, sizeof(info))) {
+			ret = -EFAULT;
+			goto err;
+		}
+
+		ret = binder_ioctl_get_freezer_info(&info);
+		if (ret < 0)
+			goto err;
+
+		if (copy_to_user(ubuf, &info, sizeof(info))) {
+			ret = -EFAULT;
+			goto err;
+		}
+		break;
+	}
 	default:
 		ret = -EINVAL;
 		goto err;
@@ -5152,6 +5205,8 @@ static void binder_deferred_release(struct binder_proc *proc)
 
 	proc->is_dead = true;
 	proc->is_frozen = false;
+	proc->sync_recv = false;
+	proc->async_recv = false;
 	threads = 0;
 	active_transactions = 0;
 	while ((n = rb_first(&proc->threads))) {
diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
index e6a53e98c6da..2872a7de68e1 100644
--- a/drivers/android/binder_internal.h
+++ b/drivers/android/binder_internal.h
@@ -376,6 +376,10 @@ struct binder_ref {
  * @is_frozen:            process is frozen and unable to service
  *                        binder transactions
  *                        (protected by @inner_lock)
+ * @sync_recv:            process received sync transactions since last frozen
+ *                        (protected by @inner_lock)
+ * @async_recv:           process received async transactions since last frozen
+ *                        (protected by @inner_lock)
  * @freeze_wait:          waitqueue of processes waiting for all outstanding
  *                        transactions to be processed
  *                        (protected by @inner_lock)
@@ -422,6 +426,8 @@ struct binder_proc {
 	int outstanding_txns;
 	bool is_dead;
 	bool is_frozen;
+	bool sync_recv;
+	bool async_recv;
 	wait_queue_head_t freeze_wait;
 
 	struct list_head todo;
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index 7eb5b818b3c1..156070d18c4f 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -223,6 +223,12 @@ struct binder_freeze_info {
 	__u32            timeout_ms;
 };
 
+struct binder_frozen_status_info {
+	__u32            pid;
+	__u32            sync_recv;
+	__u32            async_recv;
+};
+
 #define BINDER_WRITE_READ		_IOWR('b', 1, struct binder_write_read)
 #define BINDER_SET_IDLE_TIMEOUT		_IOW('b', 3, __s64)
 #define BINDER_SET_MAX_THREADS		_IOW('b', 5, __u32)
@@ -234,6 +240,7 @@ struct binder_freeze_info {
 #define BINDER_GET_NODE_INFO_FOR_REF	_IOWR('b', 12, struct binder_node_info_for_ref)
 #define BINDER_SET_CONTEXT_MGR_EXT	_IOW('b', 13, struct flat_binder_object)
 #define BINDER_FREEZE			_IOW('b', 14, struct binder_freeze_info)
+#define BINDER_GET_FROZEN_INFO		_IOWR('b', 15, struct binder_frozen_status_info)
 
 /*
  * NOTE: Two special error codes you should check for when calling
-- 
2.31.0.rc1.246.gcd05c9c855-goog

Re: [PATCH v1 1/3] binder: BINDER_FREEZE ioctl

[Greg KH]

On Wed, Mar 10, 2021 at 02:52:49PM -0800, Li Li wrote:
>  	if (target_proc) {
>  		binder_inner_proc_lock(target_proc);
> +		target_proc->outstanding_txns--;
> +		WARN_ON(target_proc->outstanding_txns < 0);

WARN_* is a huge crutch, please just handle stuff like this properly and
if you really need to, warn userspace (but what can they do about it?)

You also just rebooted all systems that have panic-on-warn set, so if
this can be triggered by userspace, you caused a DoS of things :(

So please remove all of the WARN_ON() you add in this patch series to
properly handle the error conditions and deal with them correctly.

And if these were here just for debugging, hopefully the code works
properly now and you do not need debugging anymore so they can all just
be dropped.

thanks,

greg k-h

Re: [PATCH v1 1/3] binder: BINDER_FREEZE ioctl

[Li Li]

On Wed, Mar 10, 2021 at 11:33 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Wed, Mar 10, 2021 at 02:52:49PM -0800, Li Li wrote:
> >       if (target_proc) {
> >               binder_inner_proc_lock(target_proc);
> > +             target_proc->outstanding_txns--;
> > +             WARN_ON(target_proc->outstanding_txns < 0);
>
> WARN_* is a huge crutch, please just handle stuff like this properly and
> if you really need to, warn userspace (but what can they do about it?)
>
> You also just rebooted all systems that have panic-on-warn set, so if
> this can be triggered by userspace, you caused a DoS of things :(
>
> So please remove all of the WARN_ON() you add in this patch series to
> properly handle the error conditions and deal with them correctly.
>
> And if these were here just for debugging, hopefully the code works
> properly now and you do not need debugging anymore so they can all just
> be dropped.

When the target_proc is freed, there's no outstanding transactions already.
The FREEZE ioctl from userspace won't trigger this. It's for debugging.
And I'll remove it in v2. Thanks for the suggestion!

Re: [PATCH v1 1/3] binder: BINDER_FREEZE ioctl

[Greg KH]

On Thu, Mar 11, 2021 at 01:36:26AM -0800, Li Li wrote:
> On Wed, Mar 10, 2021 at 11:33 PM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Wed, Mar 10, 2021 at 02:52:49PM -0800, Li Li wrote:
> > >       if (target_proc) {
> > >               binder_inner_proc_lock(target_proc);
> > > +             target_proc->outstanding_txns--;
> > > +             WARN_ON(target_proc->outstanding_txns < 0);
> >
> > WARN_* is a huge crutch, please just handle stuff like this properly and
> > if you really need to, warn userspace (but what can they do about it?)
> >
> > You also just rebooted all systems that have panic-on-warn set, so if
> > this can be triggered by userspace, you caused a DoS of things :(
> >
> > So please remove all of the WARN_ON() you add in this patch series to
> > properly handle the error conditions and deal with them correctly.
> >
> > And if these were here just for debugging, hopefully the code works
> > properly now and you do not need debugging anymore so they can all just
> > be dropped.
> 
> When the target_proc is freed, there's no outstanding transactions already.
> The FREEZE ioctl from userspace won't trigger this. It's for debugging.

It's ok to test for this, to verify all is good, just do not reboot
people's machines if the test fails :)

thanks,

greg k-h