witness: add tunables debug.witness.lock_order_{data_count,hash_size}
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Authored by rlibby on Mon, Jun 15, 4:02 PM.

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markj
glebius
kib

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rGca8a1c3c27b0: witness: add tunables debug.witness.lock_order_{data_count,hash_size}

Summary

Add tunable debug.witness.lock_order_data_count to allow adjusting the
number of witness lock order data entries (stacks) without recompiling
the kernel. This may help to display stacks when a lock order reversal
is reported but the number of entries is exhausted before recording the
first lock order, by allowing the user to reboot with an adjusted
tunable and try again.

Tunable debug.witness.lock_order_hash_size is also provided to allow the
hash table load factor to be managed, though that is not required.

Also tweak witness_lock_order_add to avoid computing a hash when it
won't be needed because the lock order data entries are exhausted.

Diff Detail

Repository

rG FreeBSD src repository

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Tests Skipped

Build Status

Buildable 73886
Build 70769: arc lint + arc unit

Event Timeline

rlibby created this revision.Mon, Jun 15, 4:02 PM

Herald added subscribers: olce, imp. · View Herald TranscriptMon, Jun 15, 4:02 PM

rlibby requested review of this revision.Mon, Jun 15, 4:02 PM

Harbormaster completed remote builds in B73886: Diff 179807.Mon, Jun 15, 4:02 PM

rlibby edited the test plan for this revision. (Show Details)Mon, Jun 15, 4:06 PM

rlibby added reviewers: markj, glebius, kib.

markj accepted this revision.Mon, Jun 15, 5:19 PM

markj added inline comments.

sys/kern/subr_witness.c
3435	This change isn't required for correctness, right?

This revision is now accepted and ready to land.Mon, Jun 15, 5:19 PM

rlibby added inline comments.Mon, Jun 15, 5:31 PM

sys/kern/subr_witness.c
3435	Correct. This would have a very minor performance benefit of avoiding calculating the hash when we're already out of lock order data entries. I can drop it, or move it to another commit, if you prefer.

markj added inline comments.Mon, Jun 15, 6:24 PM

sys/kern/subr_witness.c
3435	It's fine, I just wasn't sure if I was missing something. I missed the last sentence in the description.

kib accepted this revision.Tue, Jun 16, 11:36 AM

Addressing problems uncovered in testing. I had assumed that the
mechanism used by debug.witness.witness_count actually worked, but it
didn't. I added a new patch D57613 to address the problem with
witness_count by itself, and then applied that fix here too. I also
fixed an alignment problem.

This revision now requires review to proceed.Tue, Jun 16, 11:24 PM

Harbormaster completed remote builds in B73918: Diff 179888.Tue, Jun 16, 11:24 PM

markj accepted this revision.Wed, Jun 17, 1:33 PM

This revision is now accepted and ready to land.Wed, Jun 17, 1:33 PM

kib accepted this revision.Wed, Jun 17, 4:36 PM

Closed by commit rGca8a1c3c27b0: witness: add tunables debug.witness.lock_order_{data_count,hash_size} (authored by rlibby). · Explain WhyThu, Jun 18, 4:17 AM

This revision was automatically updated to reflect the committed changes.

rlibby added a commit: rGca8a1c3c27b0: witness: add tunables debug.witness.lock_order_{data_count,hash_size}.