UFS: make mkdir() and link() reliable when using SU and reaching nlink limit
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Authored by kib on Jun 18 2022, 11:07 AM.

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mckusick
jilles
jh
chs

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rG8db679af66b0: UFS: make mkdir() and link() reliable when using SU and reaching nlink limit

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PR: 165392

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kib created this revision.Jun 18 2022, 11:07 AM

Herald added a subscriber: imp. · View Herald TranscriptJun 18 2022, 11:07 AM

kib requested review of this revision.Jun 18 2022, 11:07 AM

This looks like the correct solution to me. As noted in bug report 165392, link and rename also need the same fix.

Peter Holm has a long-standing test that also triggers either this bug or one related to it. I was never able to track down the cause so it has been disabled for years but should be resurrected.

Also handle link(). Rename cannot be handled this way, and would require a separate patch.

This looks good. I concur that rename requires a different approach so can be the subject of another change.

This revision is now accepted and ready to land.Jun 19 2022, 7:11 PM

In fact the patch for link() is wrong, for the reasons similar to rename(). vpp is locked so needs to be handled around ufs_sync_nlink().

kib planned changes to this revision.Jun 19 2022, 7:21 PM

Try to fix link() handling, one more vnode is locked there.

Right. I should have noticed that something was missing in ufs_sync_nlink() when it did not include a use of vn_lock_pair(). I believe that this is now correct.

The rename system call will only have a permanent link count increase when moving a directory where the destination directory link count will increase by one. The tricky part is handling transient link count overages when a file with UFS_LINK_MAX links is moved and temporarily gets UFS_LINK_MAX + 1 until its old name is removed from its previous location. Rather than writing a lot of special purpose code to handle this very obscure case, I think we should simply not allow rename of files with UFS_LINK_MAX existing links.

This revision is now accepted and ready to land.Jun 19 2022, 10:06 PM

emaste added a subscriber: emaste.Jun 21 2022, 2:10 PM

Closed by commit rG8db679af66b0: UFS: make mkdir() and link() reliable when using SU and reaching nlink limit (authored by kib). · Explain WhyJun 22 2022, 12:36 PM

This revision was automatically updated to reflect the committed changes.

kib added a commit: rG8db679af66b0: UFS: make mkdir() and link() reliable when using SU and reaching nlink limit.