init: Set oom_score_adj to snapuserd process

When a process is started as a native service,
oom_score_adj is set to -1000 so that processes
are unkillable by lmkd.

During boot, snapuserd process is not started as a service;
hence, we need to set the oom_score_adj explicitly else in
the event of low memory situation, lmkd can kill the
process thereby device can never boot.

Bug: 234691483
Test: th and OTA on Pixel
Signed-off-by: Akilesh Kailash <akailash@google.com>
Change-Id: Ic2c85aa470522b4bc847a16b4f5cebfc528ed3cf

init/snapuserd_transition.cpp

@@ -29,6 +29,7 @@
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/parseint.h>
+#include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <cutils/sockets.h>
@@ -40,6 +41,7 @@
 #include <snapuserd/snapuserd_client.h>
 
 #include "block_dev_initializer.h"
+#include "lmkd_service.h"
 #include "service_utils.h"
 #include "util.h"
 
@@ -320,6 +322,14 @@ void SnapuserdSelinuxHelper::RelaunchFirstStageSnapuserd() {
 
         LOG(INFO) << "Relaunched snapuserd with pid: " << pid;
 
+        // Since daemon is not started as a service, we have
+        // to explicitly set the OOM score to default which is unkillable
+        std::string oom_str = std::to_string(DEFAULT_OOM_SCORE_ADJUST);
+        std::string oom_file = android::base::StringPrintf("/proc/%d/oom_score_adj", pid);
+        if (!android::base::WriteStringToFile(oom_str, oom_file)) {
+            PLOG(ERROR) << "couldn't write oom_score_adj to snapuserd daemon with pid: " << pid;
+        }
+
         if (!TestSnapuserdIsReady()) {
             PLOG(FATAL) << "snapuserd daemon failed to launch";
         } else {