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
diff --git a/recovery.cpp b/recovery.cpp
index dace52f..17e9eb6 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 @@
}
}
+// 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 @@
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;
+ }
- finish_sdcard_fuse(token);
+ 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));
+ }
+
ensure_path_unmounted(SDCARD_ROOT);
- return status;
+ return result;
}
// Return REBOOT, SHUTDOWN, or REBOOT_BOOTLOADER. Returning NO_ACTION