commit 58cc51574ac3ad571956bdb6ed056d8b24327a6f
author Josh Gao <jmgao@google.com> Tue May 19 15:57:06 2020 -0700
committer Josh Gao <jmgao@google.com> Wed May 20 21:03:18 2020 +0000
tree d6f7149153e00aa205c16b23f4c5b7fb549ae2db
parent 31ff0ca15ed28825b00df01e23447059bb682156

adb: only submit USB writes on the worker thread.

After USB disconnection, io_submit will block until the endpoint comes
back up. We handle this in the worker thread by sending it a signal to
break it out of io_submit when we notice that USB has gone down, but
opportunistic writes from the main thread can get stuck in this scenario
as well. Submitting the writes only on the worker thread doesn't have a
measurable impact on performance, so avert this scenario by only
submitting writes from the worker thread.

Bug: http://b/157078255
Test: test_device.py
Change-Id: I1118f2e2a70d13f15592eb996e7084033ed5cb9d

daemon/usb.cpp

diff --git a/daemon/usb.cpp b/daemon/usb.cpp
index 7fff05a..a663871 100644
--- a/daemon/usb.cpp
+++ b/daemon/usb.cpp
@@ -231,7 +231,14 @@
                 offset += write_size;
             }
         }
-        SubmitWrites();
+
+        // Wake up the worker thread to submit writes.
+        uint64_t notify = 1;
+        ssize_t rc = adb_write(worker_event_fd_.get(), &notify, sizeof(notify));
+        if (rc < 0) {
+            PLOG(FATAL) << "failed to notify worker eventfd to submit writes";
+        }
+
         return true;
     }
 
@@ -443,6 +450,9 @@
                 }
 
                 ReadEvents();
+
+                std::lock_guard<std::mutex> lock(write_mutex_);
+                SubmitWrites();
             }
         });
     }
@@ -626,8 +636,6 @@
         write_requests_.erase(it);
         size_t outstanding_writes = --writes_submitted_;
         LOG(DEBUG) << "USB write: reaped, down to " << outstanding_writes;
-
-        SubmitWrites();
     }
 
     IoWriteBlock CreateWriteBlock(std::shared_ptr<Block> payload, size_t offset, size_t len,