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References: <20210316011630.1121213-1-dualli@chromium.org> <20210316011630.1121213-2-dualli@chromium.org>
In-Reply-To: <20210316011630.1121213-2-dualli@chromium.org>
From:   Todd Kjos <tkjos@google.com>
Date:   Tue, 16 Mar 2021 08:28:14 -0700
Message-ID: <CAHRSSEwGCyo7Ni94jP6s27fmBmdyUK-Zj+4M044p8MYN9ggEKg@mail.gmail.com>
Subject: Re: [PATCH v3 1/3] binder: BINDER_FREEZE ioctl
To:     Li Li <dualli@chromium.org>
Cc:     Li Li <dualli@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Christian Brauner <christian@brauner.io>,
        =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>,
        "open list:ANDROID DRIVERS" <devel@driverdev.osuosl.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Martijn Coenen <maco@google.com>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Android Kernel Team <kernel-team@android.com>
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Precedence: bulk

On Mon, Mar 15, 2021 at 6:16 PM Li Li <dualli@chromium.org> wrote:
>
> 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>

For the series, you can add

Acked-by: Todd Kjos <tkjos@google.com>


> ---
>  drivers/android/binder.c            | 139 ++++++++++++++++++++++++++--
>  drivers/android/binder_internal.h   |  12 +++
>  include/uapi/linux/android/binder.h |  13 +++
>  3 files changed, 154 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index c119736ca56a..b93ca53bb90f 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1506,6 +1506,12 @@ static void binder_free_transaction(struct binder_transaction *t)
>
>         if (target_proc) {
>                 binder_inner_proc_lock(target_proc);
> +               target_proc->outstanding_txns--;
> +               if (target_proc->outstanding_txns < 0)
> +                       pr_warn("%s: Unexpected outstanding_txns %d\n",
> +                               __func__, target_proc->outstanding_txns);
> +               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 +2337,11 @@ 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 +2361,11 @@ 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)) {
>                 binder_inner_proc_unlock(proc);
>                 binder_node_unlock(node);
> -               return false;
> +               return proc->is_frozen ? BR_FROZEN_REPLY : BR_DEAD_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 +4312,9 @@ static void binder_free_proc(struct binder_proc *proc)
>
>         BUG_ON(!list_empty(&proc->todo));
>         BUG_ON(!list_empty(&proc->delivered_death));
> +       if (proc->outstanding_txns)
> +               pr_warn("%s: Unexpected outstanding_txns %d\n",
> +                       __func__, 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 +4376,7 @@ 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 +4627,45 @@ 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 +4784,66 @@ 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 +4940,7 @@ 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 +5153,7 @@ 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.rc2.261.g7f71774620-goog
>