Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210311184629.589725-1-dualli@chromium.org> <20210311184629.589725-2-dualli@chromium.org>
In-Reply-To: <20210311184629.589725-2-dualli@chromium.org>
From:   Todd Kjos <tkjos@google.com>
Date:   Fri, 12 Mar 2021 16:00:01 -0800
Message-ID: <CAHRSSEwqjJZwjWC0_6SzTkgNPKd6gNjuHVk7k5UccjFWRrsmCg@mail.gmail.com>
Subject: Re: [PATCH v2 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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Mar 11, 2021 at 10:46 AM 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>
> ---
>  drivers/android/binder.c            | 141 ++++++++++++++++++++++++++--
>  drivers/android/binder_internal.h   |  12 +++
>  include/uapi/linux/android/binder.h |  13 +++
>  3 files changed, 156 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index c119736ca56a..76ea558df03e 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);

Shouldn't this be something like "outstanding_txns is negative"? If we
ever see one of these, is this enough information to be useful? Should
we at least print the target proc's pid so someone can figure out what
process had the messed up count?

> +               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 +2361,13 @@ 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;

Do we need the proc_is_dead local? This could be:
    return proc->is_frozen ? BR_FROZEN_REPLY : BR_DEAD_REPLY

>         }
>
>         if (!thread && !pending_async)
> @@ -2373,10 +2383,11 @@ 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 +3024,16 @@ 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 +3052,9 @@ 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 +3064,8 @@ 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 +3082,6 @@ 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 +4314,9 @@ 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 +4378,7 @@ 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 +4629,45 @@ 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 +4786,66 @@ 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 +4942,7 @@ 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 +5155,7 @@ 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
>