recovery: Fork a process for fuse when sideloading from SD card.

For applying update from SD card, we used to use a thread to serve the
file with fuse. Since accessing through fuse involves going from kernel
to userspace to kernel, it may run into deadlock (e.g. for mmap_sem)
when a page fault occurs. Switch to using a process instead.

Bug: 23783099
Bug: 26313124
Change-Id: Iac0f55b1bdb078cadb520cfe1133e70fbb26eadd

fuse_sdcard_provider.cpp

@@ -18,7 +18,6 @@
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
-#include <pthread.h>
 #include <sys/mount.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -60,81 +59,30 @@ static void close_file(void* cookie) {
     close(fd->fd);
 }
 
-struct token {
-    pthread_t th;
-    const char* path;
-    int result;
-};
-
-static void* run_sdcard_fuse(void* cookie) {
-    token* t = reinterpret_cast<token*>(cookie);
-
+bool start_sdcard_fuse(const char* path) {
     struct stat sb;
-    if (stat(t->path, &sb) < 0) {
-        fprintf(stderr, "failed to stat %s: %s\n", t->path, strerror(errno));
-        t->result = -1;
-        return NULL;
+    if (stat(path, &sb) == -1) {
+        fprintf(stderr, "failed to stat %s: %s\n", path, strerror(errno));
+        return false;
     }
 
-    struct file_data fd;
-    struct provider_vtab vtab;
-
-    fd.fd = open(t->path, O_RDONLY);
-    if (fd.fd < 0) {
-        fprintf(stderr, "failed to open %s: %s\n", t->path, strerror(errno));
-        t->result = -1;
-        return NULL;
+    file_data fd;
+    fd.fd = open(path, O_RDONLY);
+    if (fd.fd == -1) {
+        fprintf(stderr, "failed to open %s: %s\n", path, strerror(errno));
+        return false;
     }
     fd.file_size = sb.st_size;
     fd.block_size = 65536;
 
+    provider_vtab vtab;
     vtab.read_block = read_block_file;
     vtab.close = close_file;
 
-    t->result = run_fuse_sideload(&vtab, &fd, fd.file_size, fd.block_size);
-    return NULL;
-}
-
-// How long (in seconds) we wait for the fuse-provided package file to
-// appear, before timing out.
-#define SDCARD_INSTALL_TIMEOUT 10
-
-void* start_sdcard_fuse(const char* path) {
-    token* t = new token;
-
-    t->path = path;
-    pthread_create(&(t->th), NULL, run_sdcard_fuse, t);
-
-    struct stat st;
-    int i;
-    for (i = 0; i < SDCARD_INSTALL_TIMEOUT; ++i) {
-        if (stat(FUSE_SIDELOAD_HOST_PATHNAME, &st) != 0) {
-            if (errno == ENOENT && i < SDCARD_INSTALL_TIMEOUT-1) {
-                sleep(1);
-                continue;
-            } else {
-                return NULL;
-            }
-        }
-    }
-
     // The installation process expects to find the sdcard unmounted.
     // Unmount it with MNT_DETACH so that our open file continues to
     // work but new references see it as unmounted.
     umount2("/sdcard", MNT_DETACH);
 
-    return t;
-}
-
-void finish_sdcard_fuse(void* cookie) {
-    if (cookie == NULL) return;
-    token* t = reinterpret_cast<token*>(cookie);
-
-    // Calling stat() on this magic filename signals the fuse
-    // filesystem to shut down.
-    struct stat st;
-    stat(FUSE_SIDELOAD_HOST_EXIT_PATHNAME, &st);
-
-    pthread_join(t->th, NULL);
-    delete t;
+    return run_fuse_sideload(&vtab, &fd, fd.file_size, fd.block_size) == 0;
 }

fuse_sdcard_provider.h

@@ -17,7 +17,6 @@
 #ifndef __FUSE_SDCARD_PROVIDER_H
 #define __FUSE_SDCARD_PROVIDER_H
 
-void* start_sdcard_fuse(const char* path);
-void finish_sdcard_fuse(void* token);
+bool start_sdcard_fuse(const char* path);
 
 #endif

recovery.cpp

@@ -28,6 +28,7 @@
 #include <sys/klog.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/wait.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -833,6 +834,10 @@ static void choose_recovery_file(Device* device) {
     }
 }
 
+// How long (in seconds) we wait for the fuse-provided package file to
+// appear, before timing out.
+#define SDCARD_INSTALL_TIMEOUT 10
+
 static int apply_from_sdcard(Device* device, bool* wipe_cache) {
     modified_flash = true;
 
@@ -850,14 +855,62 @@ static int apply_from_sdcard(Device* device, bool* wipe_cache) {
 
     ui->Print("\n-- Install %s ...\n", path);
     set_sdcard_update_bootloader_message();
-    void* token = start_sdcard_fuse(path);
 
-    int status = install_package(FUSE_SIDELOAD_HOST_PATHNAME, wipe_cache,
+    // We used to use fuse in a thread as opposed to a process. Since accessing
+    // through fuse involves going from kernel to userspace to kernel, it leads
+    // to deadlock when a page fault occurs. (Bug: 26313124)
+    pid_t child;
+    if ((child = fork()) == 0) {
+        bool status = start_sdcard_fuse(path);
+
+        _exit(status ? EXIT_SUCCESS : EXIT_FAILURE);
+    }
+
+    // FUSE_SIDELOAD_HOST_PATHNAME will start to exist once the fuse in child
+    // process is ready.
+    int result = INSTALL_ERROR;
+    int status;
+    bool waited = false;
+    for (int i = 0; i < SDCARD_INSTALL_TIMEOUT; ++i) {
+        if (waitpid(child, &status, WNOHANG) == -1) {
+            result = INSTALL_ERROR;
+            waited = true;
+            break;
+        }
+
+        struct stat sb;
+        if (stat(FUSE_SIDELOAD_HOST_PATHNAME, &sb) == -1) {
+            if (errno == ENOENT && i < SDCARD_INSTALL_TIMEOUT-1) {
+                sleep(1);
+                continue;
+            } else {
+                LOGE("Timed out waiting for the fuse-provided package.\n");
+                result = INSTALL_ERROR;
+                kill(child, SIGKILL);
+                break;
+            }
+        }
+
+        result = install_package(FUSE_SIDELOAD_HOST_PATHNAME, wipe_cache,
                                  TEMPORARY_INSTALL_FILE, false);
+        break;
+    }
+
+    if (!waited) {
+        // Calling stat() on this magic filename signals the fuse
+        // filesystem to shut down.
+        struct stat sb;
+        stat(FUSE_SIDELOAD_HOST_EXIT_PATHNAME, &sb);
+
+        waitpid(child, &status, 0);
+    }
+
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        LOGE("Error exit from the fuse process: %d\n", WEXITSTATUS(status));
+    }
 
-    finish_sdcard_fuse(token);
     ensure_path_unmounted(SDCARD_ROOT);
-    return status;
+    return result;
 }
 
 // Return REBOOT, SHUTDOWN, or REBOOT_BOOTLOADER.  Returning NO_ACTION