[LU-10824] ll_umount being improper use of cached mountpoint from mount time

• Type: Bug
• Resolution: Unresolved
• Priority: Major
• Fix Version/s: Upstream
• Affects Version/s: Lustre 2.9.0, Lustre 2.10.0, Lustre 2.11.0
• Severity: 3
• Assignee: James A Simmons
• Reporter: Oleg Drokin

Description

Al Viro chimed in complaining about patch from LU-1882 - http://review.whamcloud.com/20061
 
Basically the problem is we cache sbi->ll_mnt.mnt as

»       sbi->ll_mnt.mnt = current->fs->root.mnt;

This is prone to many errors, in particular: did not get reference count, so this mount struct might disappear, it does not take bind mounts into account not mount --move.
Might result in kernel panics in certain conditions.

Overall original patch is trying to "fix" something that's not broken in the kernel

If somebody does stat mountpoint in a tight loop, you will get -EBUSY there.
No matter what. What's more, you might very well get it after some check in
->umount_begin() has told you that at the moment the thing you were trying to
umount was not busy - just before the next stat hits.

The patch needs to be reworked and we just need to add some extra retrying logic in the test framework instead I guess.

Issue Links

• is related to: LU-12511 Prepare lustre for adoption into the linux kernel
• is related to: LU-1882 conf-sanity test_45: umount2: Device or resource busy
• is related to: LU-10467 use standard linux wait_event macros