On Thu, Jul 07, 2016 at 04:38:39PM -0700, Kamran Khan wrote: > Hi, > > I am unmounting an ext4 filesystem (Ubuntu 16.04), fuser shows that no > user-space processes are holding a handle to it: > > > root@kakhan-ubuntu:/# fuser -vm /oldroot > > USER PID ACCESS COMMAND > > /oldroot: root kernel mount /oldroot > > lsof gives this: > > > root@kakhan-ubuntu:/# lsof | grep sda > > jbd2/sda1 368 root cwd DIR 0,20 340 2 / > > jbd2/sda1 368 root rtd DIR 0,20 340 2 / > > jbd2/sda1 368 root txt unknown /proc/368/exe This is the jbd2 kernel thread for /dev/sda1; there is one of these for each mounted file system, and the thread will automatically exit with the relevant file system is umounted: unmount /dev/sda1. For example: # ps augxww | grep jbd2 root 319 0.0 0.0 0 0 ? S Jul02 0:45 [jbd2/sda3-8] root 1284 0.0 0.0 0 0 ? S Jul02 0:00 [jbd2/dm-9-8] root 1286 0.0 0.0 0 0 ? S Jul02 0:03 [jbd2/dm-8-8] root 1303 0.0 0.0 0 0 ? S Jul02 0:01 [jbd2/dm-1-8] root 1314 0.0 0.0 0 0 ? S Jul02 0:00 [jbd2/dm-10-8] root 1334 0.0 0.0 0 0 ? S Jul02 0:00 [jbd2/dm-0-8] root 7338 0.0 0.0 12748 2180 pts/3 S+ 22:32 0:00 grep jbd2 # lsof -p 319 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME jbd2/sda3 319 root cwd DIR 8,3 4096 2 / jbd2/sda3 319 root rtd DIR 8,3 4096 2 / jbd2/sda3 319 root txt unknown /proc/319/exe # lsof -p 1284 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME jbd2/dm-9 1284 root cwd DIR 8,3 4096 2 / jbd2/dm-9 1284 root rtd DIR 8,3 4096 2 / jbd2/dm-9 1284 root txt unknown /proc/1284/exe # ls -l /dev/mapper/lambda-android 0 lrwxrwxrwx. 1 root root 7 Jul 2 23:02 /dev/mapper/lambda-android -> ../dm-9 # umount /dev/mapper/lambda-android # ps augxww | grep jbd2 root 319 0.0 0.0 0 0 ? S Jul02 0:45 [jbd2/sda3-8] root 1286 0.0 0.0 0 0 ? S Jul02 0:03 [jbd2/dm-8-8] root 1303 0.0 0.0 0 0 ? S Jul02 0:01 [jbd2/dm-1-8] root 1314 0.0 0.0 0 0 ? S Jul02 0:00 [jbd2/dm-10-8] root 1334 0.0 0.0 0 0 ? S Jul02 0:00 [jbd2/dm-0-8] root 7469 0.0 0.0 12748 2184 pts/3 S+ 22:35 0:00 grep jbd2 So there's nothing wrong with the fact that you see a jbd2 thread for /dev/sda1, and that's not the reason why you are having trouble unmounting /oldroot. > I am unable to unmount the filesystem: > > > root@kakhan-ubuntu:/# umount /oldroot > > umount: /oldroot: target is busy > > (In some cases useful info about processes that > > use the device is found by lsof(8) or fuser(1).) > > Can anyone please provide some pointers on how should I proceed with > unmounting the filesystem? This is more of a VFS question than an ext4 question, and unfortunately fuser and lsof are not the only reliable ways if a file system is still busy. You might want to try searching /proc/.../mounts for any potential mountpoints on top of /oldroot that might be left over from a process which created a separate namespace, and hence wasn't affected by the umount of /oldroot/proc, or /oldroot/sys, etc. Cheers, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
