Merge cherrypicks of ['googleplex-android-review.googlesource.com/36350092'] into 25Q4-release.

Change-Id: I00c360c15772b28bf0a3bcc4918554abd1e32316
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
index 8d968c0..6477ccc 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
@@ -239,11 +239,6 @@
             return false;
         }
 
-        std::optional<std::lock_guard<std::mutex>> buffer_lock;
-        // Acquire the buffer lock at this point so that RA thread
-        // doesn't step into this buffer. See b/377819507
-        buffer_lock.emplace(snapuserd_->GetBufferLock());
-
         snapuserd_->SetMergeInProgress(ra_block_index_);
 
         loff_t offset = 0;
@@ -399,9 +394,6 @@
         // Mark the block as merge complete
         snapuserd_->SetMergeCompleted(ra_block_index_);
 
-        // Release the buffer lock
-        buffer_lock.reset();
-
         // Notify RA thread that the merge thread is ready to merge the next
         // window
         snapuserd_->NotifyRAForMergeReady();
@@ -434,11 +426,6 @@
             return false;
         }
 
-        std::optional<std::lock_guard<std::mutex>> buffer_lock;
-        // Acquire the buffer lock at this point so that RA thread
-        // doesn't step into this buffer. See b/377819507
-        buffer_lock.emplace(snapuserd_->GetBufferLock());
-
         snapuserd_->SetMergeInProgress(ra_block_index_);
 
         loff_t offset = 0;
@@ -495,9 +482,6 @@
         // Mark the block as merge complete
         snapuserd_->SetMergeCompleted(ra_block_index_);
 
-        // Release the buffer lock
-        buffer_lock.reset();
-
         // Notify RA thread that the merge thread is ready to merge the next
         // window
         snapuserd_->NotifyRAForMergeReady();
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
index 9f88f72..ab5421a 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
@@ -798,7 +798,7 @@
 
     InitializeIouring();
 
-    if (!SetThreadPriority(ANDROID_PRIORITY_BACKGROUND)) {
+    if (!SetThreadPriority(ANDROID_PRIORITY_NORMAL)) {
         SNAP_PLOG(ERROR) << "Failed to set thread priority";
     }