From cdcf28f54f085520a96f4f9e480b8df324c5decb Mon Sep 17 00:00:00 2001
From: Tao Bao <tbao@google.com>
Date: Wed, 13 Jan 2016 15:05:20 -0800
Subject: 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
---
 recovery.cpp | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 57 insertions(+), 4 deletions(-)

(limited to 'recovery.cpp')

diff --git a/recovery.cpp b/recovery.cpp
index dace52f98..17e9eb66f 100644
--- a/recovery.cpp
+++ b/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
-- 
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