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Commit bd516fe3 authored by Suren Baghdasaryan's avatar Suren Baghdasaryan
Browse files

Split the lock synchronizing LMKD socket reads/writes 

Current locking mechanism in LmkdConnection which synchronizes socket
reads and writes with socket destruction and replacement can result in
a deadlock because both read and write synchronize on the same lock.
That creates a possibility of a deadlock if the data pipe between AMS
and LMKD is full. AMS sends data to LMKD and blocks until LMKD reads
older data from the pipe to free some space for the new data. LMKD
is busy sending data to AMS and also blocks until AMS read some data
from its end of the pipe. AMS is trying to read the data from LMKD but
blocks because send operation is holding the lock they both are
synchronized on.
Change this synchonization mechanism to use two separate locks, one for
reads and one for writes so that concurrent send and receive can succeed
while preventing concurrent modifications to the socket itself.

Bug: 349702703
Change-Id: Icd4b9a2862bca8f18e213cf216d019231e0dbd2f
parent d81535a4

services/core/java/com/android/server/am/LmkdConnection.java

+45 −18
Original line number Diff line number Diff line
@@ -91,10 +91,18 @@ public class LmkdConnection { 
    @GuardedBy("mLmkdSocketLock")

    private LocalSocket mLmkdSocket = null;



    // socket I/O streams

    @GuardedBy("mLmkdSocketLock")

    // mutex to synchronize socket output stream with socket creation/destruction

    private final Object mLmkdOutputStreamLock = new Object();



    // socket output stream

    @GuardedBy("mLmkdOutputStreamLock")

    private OutputStream mLmkdOutputStream = null;

    @GuardedBy("mLmkdSocketLock")



    // mutex to synchronize socket input stream with socket creation/destruction

    private final Object mLmkdInputStreamLock = new Object();



    // socket input stream

    @GuardedBy("mLmkdInputStreamLock")

    private InputStream mLmkdInputStream = null;



    // buffer to store incoming data
@@ -148,9 +156,13 @@ public class LmkdConnection { 
                return false;

            }

            // connection established

            synchronized(mLmkdOutputStreamLock) {

                synchronized(mLmkdInputStreamLock) {

                    mLmkdSocket = socket;

                    mLmkdOutputStream = ostream;

                    mLmkdInputStream = istream;

                }

            }

            mMsgQueue.addOnFileDescriptorEventListener(mLmkdSocket.getFileDescriptor(),

                EVENT_INPUT | EVENT_ERROR,

                new MessageQueue.OnFileDescriptorEventListener() {
@@ -177,8 +189,14 @@ public class LmkdConnection { 
                mMsgQueue.removeOnFileDescriptorEventListener(

                        mLmkdSocket.getFileDescriptor());

                IoUtils.closeQuietly(mLmkdSocket);

                synchronized(mLmkdOutputStreamLock) {

                    synchronized(mLmkdInputStreamLock) {

                        mLmkdOutputStream = null;

                        mLmkdInputStream = null;

                        mLmkdSocket = null;

                    }

                }

            }

            // wake up reply waiters if any

            synchronized (mReplyBufLock) {

                if (mReplyBuf != null) {
@@ -262,25 +280,34 @@ public class LmkdConnection { 
    }



    private boolean write(ByteBuffer buf) {

        synchronized (mLmkdSocketLock) {

        boolean result = false;



        synchronized(mLmkdOutputStreamLock) {

            if (mLmkdOutputStream != null) {

                try {

                    mLmkdOutputStream.write(buf.array(), 0, buf.position());

                    result = true;

                } catch (IOException ex) {

                return false;

                }

            return true;

            }

        }



        return result;

    }



    private int read(ByteBuffer buf) {

        synchronized (mLmkdSocketLock) {

        int result = -1;



        synchronized(mLmkdInputStreamLock) {

            if (mLmkdInputStream != null) {

                try {

                return mLmkdInputStream.read(buf.array(), 0, buf.array().length);

                    result = mLmkdInputStream.read(buf.array(), 0, buf.array().length);

                } catch (IOException ex) {

                }

            return -1;

            }

        }

        return result;

    }



    /**

     * Exchange a request/reply packets with lmkd