commit a899da4e911d1c8ea1e28c9f38be9127fb4118e6
author Suren Baghdasaryan <surenb@google.com> Tue Mar 20 16:03:29 2018 -0700
committer Suren Baghdasaryan <surenb@google.com> Wed Mar 21 10:11:23 2018 -0700
tree 28311532822942c40207426a95f52cafc063ef95
parent 7d62ac1e1fcbd5490f67c217a4bb95d881303bde

lmkd: Suppress error when accessing soft_limit_in_bytes for system_server

system_server needs to register with lmkd, however it has no memory
cgroup under /dev/memcg/apps. This change detects if the process being
registered is system_server and suppresses the error message when
/dev/memcg/apps/uid_%d/pid_%d/memory.soft_limit_in_bytes file can't
be accessed.

Bug: 73483785
Test: verified logcat output
Change-Id: I03df7831f41f512ac8d3ebc46330546d08a3cbc6

lmkd/lmkd.c

diff --git a/lmkd/lmkd.c b/lmkd/lmkd.c
index 8dd4587..9163178 100644
--- a/lmkd/lmkd.c
+++ b/lmkd/lmkd.c
@@ -18,6 +18,7 @@
 
 #include <errno.h>
 #include <inttypes.h>
+#include <pwd.h>
 #include <sched.h>
 #include <signal.h>
 #include <stdbool.h>
@@ -72,6 +73,9 @@
 #define ARRAY_SIZE(x)   (sizeof(x) / sizeof(*(x)))
 #define EIGHT_MEGA (1 << 23)
 
+/* Defined as ProcessList.SYSTEM_ADJ in ProcessList.java */
+#define SYSTEM_ADJ (-900)
+
 /* default to old in-kernel interface if no memory pressure events */
 static int use_inkernel_interface = 1;
 static bool has_inkernel_module;
@@ -302,6 +306,8 @@
     char val[20];
     int soft_limit_mult;
     struct lmk_procprio params;
+    bool is_system_server;
+    struct passwd *pwdrec;
 
     lmkd_pack_get_procprio(packet, &params);
 
@@ -355,7 +361,15 @@
              "/dev/memcg/apps/uid_%d/pid_%d/memory.soft_limit_in_bytes",
              params.uid, params.pid);
     snprintf(val, sizeof(val), "%d", soft_limit_mult * EIGHT_MEGA);
-    writefilestring(path, val, true);
+
+    /*
+     * system_server process has no memcg under /dev/memcg/apps but should be
+     * registered with lmkd. This is the best way so far to identify it.
+     */
+    is_system_server = (params.oomadj == SYSTEM_ADJ &&
+                        (pwdrec = getpwnam("system")) != NULL &&
+                        params.uid == pwdrec->pw_uid);
+    writefilestring(path, val, !is_system_server);
 
     procp = pid_lookup(params.pid);
     if (!procp) {