Merge pull request #9068 from poettering/nspawn-pty-deadlock

nspawn logging deadlock fix

src/basic/log.c

@@ -1330,3 +1330,20 @@ int log_emergency_level(void) {
 
         return getpid_cached() == 1 ? LOG_EMERG : LOG_ERR;
 }
+
+int log_dup_console(void) {
+        int copy;
+
+        /* Duplicate the fd we use for fd logging if it's < 3 and use the copy from now on. This call is useful
+         * whenever we want to continue logging through the original fd, but want to rearrange stderr. */
+
+        if (console_fd >= 3)
+                return 0;
+
+        copy = fcntl(console_fd, F_DUPFD_CLOEXEC, 3);
+        if (copy < 0)
+                return -errno;
+
+        console_fd = copy;
+        return 0;
+}

src/basic/log.h

@@ -284,6 +284,8 @@ void log_set_open_when_needed(bool b);
  * stderr, the console or kmsg */
 void log_set_prohibit_ipc(bool b);
 
+int log_dup_console(void);
+
 int log_syntax_internal(
                 const char *unit,
                 int level,

src/nspawn/nspawn.c

@@ -2597,15 +2597,12 @@ static int inner_child(
                         return r;
         }
 
-        /* Now, explicitly close the log, so that we
-         * then can close all remaining fds. Closing
-         * the log explicitly first has the benefit
-         * that the logging subsystem knows about it,
-         * and is thus ready to be reopened should we
-         * need it again. Note that the other fds
-         * closed here are at least the locking and
-         * barrier fds. */
+        /* Now, explicitly close the log, so that we then can close all remaining fds. Closing the log explicitly first
+         * has the benefit that the logging subsystem knows about it, and is thus ready to be reopened should we need
+         * it again. Note that the other fds closed here are at least the locking and barrier fds. */
         log_close();
+        log_set_open_when_needed(true);
+
         (void) fdset_close_others(fds);
 
         if (arg_start_mode == START_BOOT) {
@@ -2643,9 +2640,7 @@ static int inner_child(
                 exec_target = "/bin/bash, /bin/sh";
         }
 
-        r = -errno;
-        (void) log_open();
-        return log_error_errno(r, "execv(%s) failed: %m", exec_target);
+        return log_error_errno(errno, "execv(%s) failed: %m", exec_target);
 }
 
 static int setup_sd_notify_child(void) {
@@ -2725,6 +2720,11 @@ static int outer_child(
                 if (terminal < 0)
                         return log_error_errno(terminal, "Failed to open console: %m");
 
+                /* Make sure we can continue logging to the original stderr, even if stderr points elsewhere now */
+                r = log_dup_console();
+                if (r < 0)
+                        return log_error_errno(r, "Failed to duplicate stderr: %m");
+
                 r = rearrange_stdio(terminal, terminal, terminal); /* invalidates 'terminal' on success and failure */
                 if (r < 0)
                         return log_error_errno(r, "Failed to move console to stdin/stdout/stderr: %m");