From ace01eaf6ba62423ed80bffe191dc818681805b0 Mon Sep 17 00:00:00 2001 From: Li Li Date: Thu, 26 May 2022 15:00:18 -0700 Subject: [PATCH] FROMGIT: Binder: add TF_UPDATE_TXN to replace outdated txn When the target process is busy, incoming oneway transactions are queued in the async_todo list.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 Even if the apps might only care about the lastet information, all outdated oneway transactions are still accumulated there until the frozen process is thawed later. For this kind of situations, there's no existing method to skip those outdated transactions and deliver the latest one only.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into the async_todo list of a frozen process, binder driver will check if any previous pending transactions can be superseded by comparing their code, flags and target node. If such an outdated pending transaction is found, the latest transaction will supersede that outdated one.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 Signed-off-by: Li Li Link: https://lore.kernel.org/r/20220526220018.3334775-2-dualli@chromium.org Signed-off-by: Greg Kroah-Hartman Bug: 231624308 Test: manually check async binder buffer size of frozen apps Test: stress test with kernel 4.14/4.19/5.10/5.15 (cherry picked from commit 9864bb4801331daa48514face9d0f4861e4d485b git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git char-misc-next) Change-Id: I1c4bff1eda1ca15aaaad5bf696c8fc00be743176 --- drivers/android/binder.c | 78 +++++++++++++++++++++++++++++ drivers/android/binder_trace.h | 4 ++ include/uapi/linux/android/binder.h | 1 + 3 files changed, 83 insertions(+) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 0cbaee418ea0..336a13ff60a9 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2495,6 +2495,56 @@ static int binder_fixup_parent(struct binder_transaction *t, return 0; } +/** + * 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 @@ -2520,6 +2570,7 @@ 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); @@ -2557,6 +2608,17 @@ static int binder_proc_transaction(struct binder_transaction *t, } else if (!pending_async) { binder_enqueue_work_ilocked(&t->work, &proc->todo); } 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); } @@ -2567,6 +2629,22 @@ 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 a70e23716ad0..8c4a6c3774a1 100644 --- a/drivers/android/binder_trace.h +++ b/drivers/android/binder_trace.h @@ -306,6 +306,10 @@ 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), diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h index 2d3f015e2ae3..7badb670f24f 100644 --- a/include/uapi/linux/android/binder.h +++ b/include/uapi/linux/android/binder.h @@ -319,6 +319,7 @@ enum transaction_flags { TF_STATUS_CODE = 0x08, /* contents are a 32-bit status code */ TF_ACCEPT_FDS = 0x10, /* allow replies with file descriptors */ TF_CLEAR_BUF = 0x20, /* clear buffer on txn complete */ + TF_UPDATE_TXN = 0x40, /* update the outdated pending async txn */ }; struct binder_transaction_data {