Remove VV_CROSSLOCK flag, and logic in nullfs and unionfs
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Authored by olce on Jul 3 2023, 12:53 PM.

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Reviewers

jah
mjg
kib
markj

Summary

This commit is part of a series whose goal is to remove the VV_CROSSLOCK vnode
flag and logic and fix a timing-dependent deadlock between lookup and unmount.

Diff Detail

Repository

rG FreeBSD src repository

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Build Status

Buildable 52839
Build 49730: arc lint + arc unit

Event Timeline

olce created this revision.Jul 3 2023, 12:53 PM

Herald added a subscriber: imp. · View Herald TranscriptJul 3 2023, 12:53 PM

olce requested review of this revision.Jul 3 2023, 12:53 PM

Harbormaster completed remote builds in B52402: Diff 124122.Jul 3 2023, 12:53 PM

olce added a parent revision: D40851: vfs_lookup(): Use vn_cross_mounts() to cross mount points.Jul 3 2023, 1:03 PM

olce added a child revision: D40853: Bump __FreeBSD_version after mount crossing semantics change.

emaste added a subscriber: emaste.Jul 17 2023, 4:10 PM

jah added inline comments.Jul 23 2023, 6:39 PM

sys/fs/unionfs/union_vfsops.c
326–327	This will no longer hold true with the new locking protocol, will it? The lookup path should go back to its old pre-VV_CROSSLOCK behavior of dropping the covered vnode lock before calling VFS_ROOT() to lock the next vnode in the mount chain while holding mp busy (though it seems the exact details here might change depending on the outcome of your conversation with mjg@)

Remove an obsolete comment about a remaining LOR in unionfs on below mounts.

Harbormaster completed remote builds in B52839: Diff 125156.Jul 25 2023, 8:59 PM

olce marked an inline comment as done.Jul 25 2023, 8:59 PM

olce added inline comments.

sys/fs/unionfs/union_vfsops.c
326–327	Indeed. Not sure why I didn't remove this part of the comment from the start. This should be true with mjg@'s proposal as well, even if it differs in the way to avoid locking both the covered and root vnode at the same time.