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authorLi Li <dualli@google.com>2022-05-27 00:00:18 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-06-27 16:16:30 +0200
commit9864bb4801331daa48514face9d0f4861e4d485b (patch)
treea4f8e9cb3b6a8faa547afe5b6e42c12c894dad18 /drivers/android
parentlkdtm: cfi: use NULL for a null pointer rather than zero (diff)
downloadlinux-9864bb4801331daa48514face9d0f4861e4d485b.tar.xz
linux-9864bb4801331daa48514face9d0f4861e4d485b.zip
Binder: add TF_UPDATE_TXN to replace outdated txn
When the target process is busy, incoming oneway transactions are queued in the async_todo list. If the clients continue sending extra oneway transactions while the target process is frozen, this queue can become too large to accommodate new transactions. That's why binder driver introduced ONEWAY_SPAM_DETECTION to detect this situation. It's helpful to debug the async binder buffer exhausting issue, but the issue itself isn't solved directly. In real cases applications are designed to send oneway transactions repeatedly, delivering updated inforamtion to the target process. Typical examples are Wi-Fi signal strength and some real time sensor data. Even if the apps might only care about the lastet information, all outdated oneway transactions are still accumulated there until the frozen process is thawed later. For this kind of situations, there's no existing method to skip those outdated transactions and deliver the latest one only. This patch introduces a new transaction flag TF_UPDATE_TXN. To use it, use apps can set this new flag along with TF_ONE_WAY. When such an oneway transaction is to be queued into the async_todo list of a frozen process, binder driver will check if any previous pending transactions can be superseded by comparing their code, flags and target node. If such an outdated pending transaction is found, the latest transaction will supersede that outdated one. This effectively prevents the async binder buffer running out and saves unnecessary binder read workloads. Acked-by: Todd Kjos <tkjos@google.com> Signed-off-by: Li Li <dualli@google.com> Link: https://lore.kernel.org/r/20220526220018.3334775-2-dualli@chromium.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/android')
-rw-r--r--drivers/android/binder.c85
-rw-r--r--drivers/android/binder_trace.h4
2 files changed, 86 insertions, 3 deletions
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 362c0deb65f1..d4f84f25c30b 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2627,6 +2627,56 @@ static int binder_fixup_parent(struct list_head *pf_head,
}
/**
+ * binder_can_update_transaction() - Can a txn be superseded by an updated one?
+ * @t1: the pending async txn in the frozen process
+ * @t2: the new async txn to supersede the outdated pending one
+ *
+ * Return: true if t2 can supersede t1
+ * false if t2 can not supersede t1
+ */
+static bool binder_can_update_transaction(struct binder_transaction *t1,
+ struct binder_transaction *t2)
+{
+ if ((t1->flags & t2->flags & (TF_ONE_WAY | TF_UPDATE_TXN)) !=
+ (TF_ONE_WAY | TF_UPDATE_TXN) || !t1->to_proc || !t2->to_proc)
+ return false;
+ if (t1->to_proc->tsk == t2->to_proc->tsk && t1->code == t2->code &&
+ t1->flags == t2->flags && t1->buffer->pid == t2->buffer->pid &&
+ t1->buffer->target_node->ptr == t2->buffer->target_node->ptr &&
+ t1->buffer->target_node->cookie == t2->buffer->target_node->cookie)
+ return true;
+ return false;
+}
+
+/**
+ * binder_find_outdated_transaction_ilocked() - Find the outdated transaction
+ * @t: new async transaction
+ * @target_list: list to find outdated transaction
+ *
+ * Return: the outdated transaction if found
+ * NULL if no outdated transacton can be found
+ *
+ * Requires the proc->inner_lock to be held.
+ */
+static struct binder_transaction *
+binder_find_outdated_transaction_ilocked(struct binder_transaction *t,
+ struct list_head *target_list)
+{
+ struct binder_work *w;
+
+ list_for_each_entry(w, target_list, entry) {
+ struct binder_transaction *t_queued;
+
+ if (w->type != BINDER_WORK_TRANSACTION)
+ continue;
+ t_queued = container_of(w, struct binder_transaction, work);
+ if (binder_can_update_transaction(t_queued, t))
+ return t_queued;
+ }
+ return NULL;
+}
+
+/**
* binder_proc_transaction() - sends a transaction to a process and wakes it up
* @t: transaction to send
* @proc: process to send the transaction to
@@ -2651,6 +2701,7 @@ static int binder_proc_transaction(struct binder_transaction *t,
struct binder_node *node = t->buffer->target_node;
bool oneway = !!(t->flags & TF_ONE_WAY);
bool pending_async = false;
+ struct binder_transaction *t_outdated = NULL;
BUG_ON(!node);
binder_node_lock(node);
@@ -2678,12 +2729,24 @@ static int binder_proc_transaction(struct binder_transaction *t,
if (!thread && !pending_async)
thread = binder_select_thread_ilocked(proc);
- if (thread)
+ if (thread) {
binder_enqueue_thread_work_ilocked(thread, &t->work);
- else if (!pending_async)
+ } else if (!pending_async) {
binder_enqueue_work_ilocked(&t->work, &proc->todo);
- else
+ } else {
+ if ((t->flags & TF_UPDATE_TXN) && proc->is_frozen) {
+ t_outdated = binder_find_outdated_transaction_ilocked(t,
+ &node->async_todo);
+ if (t_outdated) {
+ binder_debug(BINDER_DEBUG_TRANSACTION,
+ "txn %d supersedes %d\n",
+ t->debug_id, t_outdated->debug_id);
+ list_del_init(&t_outdated->work.entry);
+ proc->outstanding_txns--;
+ }
+ }
binder_enqueue_work_ilocked(&t->work, &node->async_todo);
+ }
if (!pending_async)
binder_wakeup_thread_ilocked(proc, thread, !oneway /* sync */);
@@ -2692,6 +2755,22 @@ static int binder_proc_transaction(struct binder_transaction *t,
binder_inner_proc_unlock(proc);
binder_node_unlock(node);
+ /*
+ * To reduce potential contention, free the outdated transaction and
+ * buffer after releasing the locks.
+ */
+ if (t_outdated) {
+ struct binder_buffer *buffer = t_outdated->buffer;
+
+ t_outdated->buffer = NULL;
+ buffer->transaction = NULL;
+ trace_binder_transaction_update_buffer_release(buffer);
+ binder_transaction_buffer_release(proc, NULL, buffer, 0, 0);
+ binder_alloc_free_buf(&proc->alloc, buffer);
+ kfree(t_outdated);
+ binder_stats_deleted(BINDER_STAT_TRANSACTION);
+ }
+
return 0;
}
diff --git a/drivers/android/binder_trace.h b/drivers/android/binder_trace.h
index 8eeccdc64724..8cc07e6a4273 100644
--- a/drivers/android/binder_trace.h
+++ b/drivers/android/binder_trace.h
@@ -311,6 +311,10 @@ DEFINE_EVENT(binder_buffer_class, binder_transaction_failed_buffer_release,
TP_PROTO(struct binder_buffer *buffer),
TP_ARGS(buffer));
+DEFINE_EVENT(binder_buffer_class, binder_transaction_update_buffer_release,
+ TP_PROTO(struct binder_buffer *buffer),
+ TP_ARGS(buffer));
+
TRACE_EVENT(binder_update_page_range,
TP_PROTO(struct binder_alloc *alloc, bool allocate,
void __user *start, void __user *end),