[LU-17412] lustre snapshot: write barrier stuck at "failed" state

Related — Thu, 11 Jan 2024 09:06:09 +0000

When we create a lustre snapshot (lctl snapshot_create) a global write barrier is used internally to avoid an inconsistent snapshot of the filesystem.

Creating a snapshot after mounting another snapshot causes the barrier to get into a "failed" state. This state cannot be cleared until an MGS remount an actual filesystem. Any operations involving barrier fails due to this<lctl snapshot_{create, destroy} >, etc.

# lctl barrier_stat testfs
state: failed
timeout: 0 seconds

# lctl barrier_rescan testfs
Fail to rescan barrier bitmap for testfs: Invalid argument
# lctl barrier_thaw testfs
Fail to thaw barrier for testfs: Invalid argument

Bisecting through master branch recent commits. The below commit was causing the issue and I'm not able to reproduce this issue without this commit.

    LU-17142 mgc: reconnection without pinger

Overall looks like the issue is due to ~~LU-17142~~.

I'm able to consistently reproduce this using this script(reproducer.sh).

Whamcloud Community JIRA

[LU-17412] lustre snapshot: write barrier stuck at "failed" state