Several fixes for nullfs and fifofs
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Authored by kib on Jul 26 2021, 5:11 PM.

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Reviewers

jah
markj

Commits

rG4eaf9609fe42: nullfs: provide custom null_rename bypass
rG26e72728ce12: null_rename: some style
rG10db1896495b: fifofs: fifo vnode might be relocked before VOP_OPEN() is called
rG4f21442e10db: null_lookup: restore dvp lock always, not only on success
rGd5b078163e0d: null_bypass(): prevent loosing the only reference to the lower vnode
rG161e9a97363d: nullfs: provide custom null_advlock bypass
rG7b7227c4a601: null_bypass(): some style

Summary

Nullfs: tolerate relocking of the lower vnode. We need to acquire additional hold reference on the lower vnode, otherwise is lower is relocked and upper is reclaimed, the only reference to lower is invalidated and lowervp is potentially dandling pointer.

Nullfs: provide custom bypass methods for several VOPs which take unlocked vnode. Default bypass cannot handle reclamation. Relevant for VOP_ADVLOCK, VOP_RENAME at least.

Nullfs: re-lock dvp in null_lookup() always, not only on success. Lower lookup might have relocked lowerdvp, which makes upper vp loosing its lock.

Nullfs: style fixes

Fifofs: handle race with relocking in open. It is possible that open relocks fifofs vnode after instantiation but before VOP_OPEN() is called. In this case reclaim/fifo_close() would legitimately see NULL v_fifoinfo.

Reported and tested by: pho

Per commit view is avaiable at https://kib.kiev.ua/git/gitweb.cgi?p=deviant3.git;a=shortlog;h=refs/heads/nullfs

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rG FreeBSD src repository

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Event Timeline

kib requested review of this revision.Jul 26 2021, 5:11 PM

kib created this revision.

kib edited the summary of this revision. (Show Details)

kib added a reviewer: markj.

markj added inline comments.Jul 27 2021, 2:00 PM

sys/fs/nullfs/null_vnops.c
255
355
698	How do we know that tdnn and tnn are not NULL?

kib marked 3 inline comments as done.Jul 27 2021, 2:27 PM

kib added inline comments.

sys/fs/nullfs/null_vnops.c
698	tdvp and (optional) tvp are locked on VOP entry, and we checked that there is no cross-mount rename at the start of the VOP. Since vnodes are locked (and not doomed), their lower vnodes must be alive.