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Subject[PATCH 15/37] binder: don't modify thread->looper from other threads
Date
The looper member of struct binder_thread is a bitmask
of control bits. All of the existing bits are modified
by the affected thread except for BINDER_LOOPER_STATE_NEED_RETURN
which can be modified in binder_deferred_flush() by
another thread.

To avoid adding a spinlock around all read-mod-writes to
modify a bit, the BINDER_LOOPER_STATE_NEED_RETURN flag
is replaced by a separate field in struct binder_thread.

Signed-off-by: Todd Kjos <tkjos@google.com>
---
drivers/android/binder.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 71faf548482d..3c1129d91825 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -334,14 +334,14 @@ enum {
BINDER_LOOPER_STATE_EXITED = 0x04,
BINDER_LOOPER_STATE_INVALID = 0x08,
BINDER_LOOPER_STATE_WAITING = 0x10,
- BINDER_LOOPER_STATE_NEED_RETURN = 0x20
};

struct binder_thread {
struct binder_proc *proc;
struct rb_node rb_node;
int pid;
- int looper;
+ int looper; /* only modified by this thread */
+ bool looper_need_return; /* can be written by other thread */
struct binder_transaction *transaction_stack;
struct list_head todo;
uint32_t return_error; /* Write failed, return error code in read buf */
@@ -2276,14 +2276,13 @@ static void binder_stat_br(struct binder_proc *proc,
static int binder_has_proc_work(struct binder_proc *proc,
struct binder_thread *thread)
{
- return !list_empty(&proc->todo) ||
- (thread->looper & BINDER_LOOPER_STATE_NEED_RETURN);
+ return !list_empty(&proc->todo) || thread->looper_need_return;
}

static int binder_has_thread_work(struct binder_thread *thread)
{
return !list_empty(&thread->todo) || thread->return_error != BR_OK ||
- (thread->looper & BINDER_LOOPER_STATE_NEED_RETURN);
+ thread->looper_need_return;
}

static int binder_put_node_cmd(struct binder_proc *proc,
@@ -2412,8 +2411,7 @@ static int binder_thread_read(struct binder_proc *proc,
entry);
} else {
/* no data added */
- if (ptr - buffer == 4 &&
- !(thread->looper & BINDER_LOOPER_STATE_NEED_RETURN))
+ if (ptr - buffer == 4 && !thread->looper_need_return)
goto retry;
break;
}
@@ -2727,7 +2725,7 @@ static struct binder_thread *binder_get_thread(struct binder_proc *proc)
INIT_LIST_HEAD(&thread->todo);
rb_link_node(&thread->rb_node, parent, p);
rb_insert_color(&thread->rb_node, &proc->threads);
- thread->looper |= BINDER_LOOPER_STATE_NEED_RETURN;
+ thread->looper_need_return = true;
thread->return_error = BR_OK;
thread->return_error2 = BR_OK;
}
@@ -2983,7 +2981,7 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
ret = 0;
err:
if (thread)
- thread->looper &= ~BINDER_LOOPER_STATE_NEED_RETURN;
+ thread->looper_need_return = false;
binder_unlock(__func__);
wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret && ret != -ERESTARTSYS)
@@ -3138,7 +3136,7 @@ static void binder_deferred_flush(struct binder_proc *proc)
for (n = rb_first(&proc->threads); n != NULL; n = rb_next(n)) {
struct binder_thread *thread = rb_entry(n, struct binder_thread, rb_node);

- thread->looper |= BINDER_LOOPER_STATE_NEED_RETURN;
+ thread->looper_need_return = true;
if (thread->looper & BINDER_LOOPER_STATE_WAITING) {
wake_up_interruptible(&thread->wait);
wake_count++;
@@ -3399,7 +3397,9 @@ static void print_binder_thread(struct seq_file *m,
size_t start_pos = m->count;
size_t header_pos;

- seq_printf(m, " thread %d: l %02x\n", thread->pid, thread->looper);
+ seq_printf(m, " thread %d: l %02x need_return %d\n",
+ thread->pid, thread->looper,
+ thread->looper_need_return);
header_pos = m->count;
t = thread->transaction_stack;
while (t) {
--
2.13.2.725.g09c95d1e9-goog
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