lmkd: Add hooks to LMKD

Adds several hooks to LMKD that can be overridden by the vendor. This
allows for device specific control of LMKD when necessary.

Bug: b/210075795
Test: cq

Change-Id: Ib231743183134b05148d45d681765860da6274ae
(cherry picked from commit 2c1248381a52fc520c6cd1acfaee80818eaa9ee1)
Merged-In: Ib231743183134b05148d45d681765860da6274ae

Android.bp

@@ -2,6 +2,32 @@ package {
     default_applicable_licenses: ["Android-Apache-2.0"],
 }
 
+soong_config_module_type {
+    name: "lmkd_hooks_cc_defaults",
+    module_type: "cc_defaults",
+    config_namespace: "lmkd",
+    bool_variables: ["use_hooks"],
+    properties: [
+        "cflags",
+        "static_libs",
+    ],
+}
+
+lmkd_hooks_cc_defaults {
+    name: "lmkd_hooks_defaults",
+
+    soong_config_variables: {
+        use_hooks: {
+            cflags: [
+                "-DLMKD_USE_HOOKS"
+            ],
+            static_libs: [
+                "liblmkdhooks"
+            ]
+        }
+    }
+}
+
 cc_defaults {
     name: "stats_defaults",
     cflags: [
@@ -38,7 +64,7 @@ cc_binary {
         "-DLMKD_TRACE_KILLS"
     ],
     init_rc: ["lmkd.rc"],
-    defaults: ["stats_defaults"],
+    defaults: ["stats_defaults", "lmkd_hooks_defaults"],
     logtags: ["event.logtags"],
     afdo: true,
 }

include/lmkd_hooks.h

@@ -0,0 +1,67 @@
+/*
+ *  Copyright 2022 Google, Inc
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+/*
+ * This file defines no-op hook functions for LMKD. To override these
+ * definitions, enable the use_lmkd_hooks product variable and create a library
+ * "liblmkdhooks" that supplies definitions for the hook functions in your
+ * vendor folder.
+ */
+
+#ifndef _LMKD_HOOKS_H_
+#define _LMKD_HOOKS_H_
+
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+#ifdef LMKD_USE_HOOKS
+
+/*
+ * Initialize all necessary Android props and perform any necessary validation
+ * on the values. Called before lmkd_init_hook() and will be called again
+ * whenever LMKD receives the LMK_UPDATE_PROPS command. Returns true on success,
+ * false otherwise.
+ */
+bool lmkd_update_props_hook();
+/*
+ * Perform any necessary initialization for the hooks. Called only once at the
+ * end of LMKD's init(). Returns true on success, false otherwise.
+ */
+bool lmkd_init_hook();
+/*
+ * Allows for interception of a kill by LMKD. This hook may attempt to free
+ * memory elsewhere to avoid the specified process being killed. Returns 0 to
+ * proceed with the kill, or the number of memory pages freed elsewhere to skip
+ * the kill.
+ */
+int lmkd_free_memory_before_kill_hook(struct proc* procp, int proc_size_pages,
+                                      int proc_oom_score, int kill_reason);
+
+#else /* LMKD_USE_HOOKS */
+
+static inline bool lmkd_update_props_hook() { return true; }
+static inline bool lmkd_init_hook() { return true; }
+static inline int lmkd_free_memory_before_kill_hook(struct proc*, int, int,
+                                                    int) {
+  return 0;
+}
+
+#endif /* LMKD_USE_HOOKS */
+
+__END_DECLS
+
+#endif

lmkd.cpp

@@ -42,6 +42,7 @@
 #include <cutils/sockets.h>
 #include <liblmkd_utils.h>
 #include <lmkd.h>
+#include <lmkd_hooks.h>
 #include <log/log.h>
 #include <log/log_event_list.h>
 #include <log/log_time.h>
@@ -547,7 +548,7 @@ static uint32_t killcnt_total = 0;
 /* PAGE_SIZE / 1024 */
 static long page_k;
 
-static void update_props();
+static bool update_props();
 static bool init_monitors();
 static void destroy_monitors();
 
@@ -1512,14 +1513,19 @@ static void ctrl_command_handler(int dsock_idx) {
     case LMK_UPDATE_PROPS:
         if (nargs != 0)
             goto wronglen;
-        update_props();
+        result = -1;
+        if (update_props()) {
             if (!use_inkernel_interface) {
                 /* Reinitialize monitors to apply new settings */
                 destroy_monitors();
-            result = init_monitors() ? 0 : -1;
+                if (init_monitors()) {
+                    result = 0;
+                }
             } else {
                 result = 0;
             }
+        }
+
         len = lmkd_pack_set_update_props_repl(packet, result);
         if (ctrl_data_write(dsock_idx, (char *)packet, len) != len) {
             ALOGE("Failed to report operation results");
@@ -2320,6 +2326,17 @@ static int kill_one_process(struct proc* procp, int min_oom_score, struct kill_i
     snprintf(desc, sizeof(desc), "lmk,%d,%d,%d,%d,%d", pid, ki ? (int)ki->kill_reason : -1,
              procp->oomadj, min_oom_score, ki ? ki->max_thrashing : -1);
 
+    result = lmkd_free_memory_before_kill_hook(procp, rss_kb / page_k, min_oom_score,
+                                               ki->kill_reason);
+    if (result > 0) {
+      /*
+       * Memory was freed elsewhere; no need to kill. Note: intentionally do not
+       * pid_remove(pid) since it was not killed.
+       */
+      ALOGI("Skipping kill; %ld kB freed elsewhere.", result * page_k);
+      return result;
+    }
+
     trace_kill_start(pid, desc);
 
     start_wait_for_proc_kill(pidfd < 0 ? pid : pidfd);
@@ -3462,6 +3479,11 @@ static int init(void) {
     }
     ALOGI("Process polling is %s", pidfd_supported ? "supported" : "not supported" );
 
+    if (!lmkd_init_hook()) {
+        ALOGE("Failed to initialize LMKD hooks.");
+        return -1;
+    }
+
     return 0;
 }
 
@@ -3649,7 +3671,7 @@ int issue_reinit() {
     return res == UPDATE_PROPS_SUCCESS ? 0 : -1;
 }
 
-static void update_props() {
+static bool update_props() {
     /* By default disable low level vmpressure events */
     level_oomadj[VMPRESS_LEVEL_LOW] =
         GET_LMK_PROPERTY(int32, "low", OOM_SCORE_ADJ_MAX + 1);
@@ -3693,6 +3715,14 @@ static void update_props() {
     stall_limit_critical = GET_LMK_PROPERTY(int64, "stall_limit_critical", 100);
 
     reaper.enable_debug(debug_process_killing);
+
+    /* Call the update props hook */
+    if (!lmkd_update_props_hook()) {
+        ALOGE("Failed to update LMKD hook props.");
+        return false;
+    }
+
+    return true;
 }
 
 int main(int argc, char **argv) {
@@ -3703,7 +3733,10 @@ int main(int argc, char **argv) {
         return issue_reinit();
     }
 
-    update_props();
+    if (!update_props()) {
+        ALOGE("Failed to initialize props, exiting.");
+        return -1;
+    }
 
     ctx = create_android_logger(KILLINFO_LOG_TAG);