From b877c3b06f15a025748b9f09621ddf1bd00cacce Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 20 Dec 2019 17:58:03 +0100
Subject: [PATCH] umount: check LO_FLAGS_AUTOCLEAR after LOOP_CLR_FD claimed
 success

Fixes: #14410
Replaces: #14386

---
 systemd-239/src/core/umount.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/core/umount.c b/src/core/umount.c
index 241fe6f..4400b3c 100644
--- a/src/core/umount.c
+++ b/src/core/umount.c
@@ -334,23 +334,38 @@ static int dm_list_get(MountPoint **head) {
 
 static int delete_loopback(const char *device) {
         _cleanup_close_ int fd = -1;
-        int r;
+        struct loop_info64 info;
 
         assert(device);
 
         fd = open(device, O_RDONLY|O_CLOEXEC);
         if (fd < 0)
                 return errno == ENOENT ? 0 : -errno;
+        
+        if (ioctl(fd, LOOP_CLR_FD, 0) < 0) {
+                if (errno == ENXIO) /* Nothing bound, didn't do anything */
+                        return 0;
+
+                return -errno;
+        }
 
-        r = ioctl(fd, LOOP_CLR_FD, 0);
-        if (r >= 0)
+        if (ioctl(fd, LOOP_GET_STATUS64, &info) < 0) {
+                /* If the LOOP_CLR_FD above succeeded we'll see ENXIO here. */
+                if (errno == ENXIO)
+                        log_debug("Successfully detached loopback device %s.", device);
+                else
+                        log_debug_errno(errno, "Failed to invoke LOOP_GET_STATUS64 on loopback device %s, ignoring: %m", device); /* the LOOP_CLR_FD at least worked, let's hope for the best */
                 return 1;
+        }
 
-        /* ENXIO: not bound, so no error */
-        if (errno == ENXIO)
-                return 0;
+        /* Linux makes LOOP_CLR_FD succeed whenever LO_FLAGS_AUTOCLEAR is set without actually doing
+         * anything. Very confusing. Let's hence not claim we did anything in this case. */
+        if (FLAGS_SET(info.lo_flags, LO_FLAGS_AUTOCLEAR))
+                log_debug("Successfully called LOOP_CLR_FD on a loopback device %s with autoclear set, which is a NOP.", device);
+        else
+                log_debug("Weird, LOOP_CLR_FD succeeded but the device is still attached on %s.", device);
 
-        return -errno;
+        return -EBUSY; /* Nothing changed, the device is still attached, hence it apparently is still busy */;
 }
 
 static int delete_dm(dev_t devnum) {
-- 
2.31.1