commit bc25d738bcee89b832eb7ec34947a19851bbe28c
author Josh Gao <jmgao@google.com> Tue May 19 15:57:06 2020 -0700
committer Josh Gao <jmgao@google.com> Thu May 21 14:55:46 2020 -0700
tree 68e2dd2ef98d072557ed61780cf6ae0749b73be1
parent 232c75651bb628e887f0d9c5a6ed6fe2a5267d86

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
(cherry picked from commit 962551000b46a47e640ca0e7b719c66b721233ae)

adb/daemon/usb.cpp

diff --git a/adb/daemon/usb.cpp b/adb/daemon/usb.cpp
index 7fff05a..a663871 100644
--- a/adb/daemon/usb.cpp
+++ b/adb/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,