lmkd: Implement pid purge command to clear old pids when zygote restarts

lmkd keeps a list of pids registered by ActivityManager, however on rare
occasions when framework restarts and lmkd survives that list has to be
purged. Implement a command that can be used to clear the pid list.

Bug: 116801366
Test: locally by killing zygote process
Change-Id: I71d6012f86bb83a73edd5b687e05a0848e0569b1
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

lmkd/include/lmkd.h

@@ -30,6 +30,7 @@ enum lmk_cmd {
     LMK_TARGET = 0,  /* Associate minfree with oom_adj_score */
     LMK_PROCPRIO,    /* Register a process and set its oom_adj_score */
     LMK_PROCREMOVE,  /* Unregister a process */
+    LMK_PROCPURGE,   /* Purge all registered processes */
 };
 
 /*
@@ -142,6 +143,15 @@ inline size_t lmkd_pack_set_procremove(LMKD_CTRL_PACKET packet,
     return 2 * sizeof(int);
 }
 
+/*
+ * Prepare LMK_PROCPURGE packet and return packet size in bytes.
+ * Warning: no checks performed, caller should ensure valid parameters.
+ */
+inline size_t lmkd_pack_set_procpurge(LMKD_CTRL_PACKET packet) {
+    packet[0] = htonl(LMK_PROCPURGE);
+    return sizeof(int);
+}
+
 __END_DECLS
 
 #endif /* _LMKD_H_ */

lmkd/lmkd.c

@@ -619,6 +619,31 @@ static void cmd_procremove(LMKD_CTRL_PACKET packet) {
     pid_remove(params.pid);
 }
 
+static void cmd_procpurge() {
+    int i;
+    struct proc *procp;
+    struct proc *next;
+
+    if (use_inkernel_interface) {
+        return;
+    }
+
+    for (i = 0; i <= ADJTOSLOT(OOM_SCORE_ADJ_MAX); i++) {
+        procadjslot_list[i].next = &procadjslot_list[i];
+        procadjslot_list[i].prev = &procadjslot_list[i];
+    }
+
+    for (i = 0; i < PIDHASH_SZ; i++) {
+        procp = pidhash[i];
+        while (procp) {
+            next = procp->pidhash_next;
+            free(procp);
+            procp = next;
+        }
+    }
+    memset(&pidhash[0], 0, sizeof(pidhash));
+}
+
 static void cmd_target(int ntargets, LMKD_CTRL_PACKET packet) {
     int i;
     struct lmk_target target;
@@ -761,6 +786,11 @@ static void ctrl_command_handler(int dsock_idx) {
             goto wronglen;
         cmd_procremove(packet);
         break;
+    case LMK_PROCPURGE:
+        if (nargs != 0)
+            goto wronglen;
+        cmd_procpurge();
+        break;
     default:
         ALOGE("Received unknown command code %d", cmd);
         return;