linux-kernel - [PATCH v6 0/6] locking/lockdep: Reuse zapped chain

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Date:   Thu,  6 Feb 2020 10:24:02 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org, Bart Van Assche <bvanassche@....org>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v6 0/6] locking/lockdep: Reuse zapped chain_hlocks entries

 v6:
  - Drop patch 7 for now.
  - Incorporate further changes as suggested by PeterZ.
  - Increase MAX_CHAIN_BUCKETS to 16 to further minimize the possibility
    of having more than one chain block in bucket 0.

 v5:
  - Fix more build errors reported by kbuild test robot.

 v4:
  - Fix build errors reported by kbuild test robot.
  - Adopt the single chain block allocator code suggested by PeterZ which
    combine the last 3 patches of v3 series.
  - Add another patch to introduce a fast path in the chain block
    allocator.
  - In patch 1, move the inc_chains() out of CONFIG_TRACE_IRQFLAGS
    conditional compilation block.

 v3:
  - Move the bug fix patches to the beginning of the series.
  - Include a number of changes as suggested by PeterZ.
  - Increase MAX_CHAIN_BUCKETS from 8 to 10 to reduce the chance of using
    the unsized list.
  - Add patch 7 to add a lockdep_early_init() call.
  - Add patch 8 to allocate chain hlocks by splitting large chain block
    as a last resort.

 v2:
  - Revamp the chain_hlocks reuse patch to store the freed chain_hlocks
    information in the chain_hlocks entries themselves avoiding the
    need of a separate set of tracking structures. This, however,
    requires a minimum allocation size of at least 2. Thanks to PeterZ
    for his review and inspiring this change.
  - Remove the leakage counter as it is no longer applicable.
  - Add patch 6 to make the output of /proc/lockdep_chains more readable.

It was found that when running a workload that kept on adding lock
classes and then zapping them repetitively, the system will eventually
run out of chain_hlocks[] entries even though there were still plenty
of other lockdep data buffers available.

  [ 4318.443670] BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
  [ 4318.444809] turning off the locking correctness validator.

In order to fix this problem, we have to make chain_hlocks[] entries
reusable just like other lockdep arrays. Besides that, the patchset
also adds some zapped class and chain_hlocks counters to be tracked by
/proc/lockdep_stats. It also fixes leakage in the irq context counters
and makes the output of /proc/lockdep_chains more readable.

Waiman Long (6):
  locking/lockdep: Decrement irq context counters when removing lock
    chain
  locking/lockdep: Display irq_context names in /proc/lockdep_chains
  locking/lockdep: Track number of zapped classes
  locking/lockdep: Throw away all lock chains with zapped class
  locking/lockdep: Track number of zapped lock chains
  locking/lockdep: Reuse freed chain_hlocks entries

 kernel/locking/lockdep.c           | 332 ++++++++++++++++++++++++-----
 kernel/locking/lockdep_internals.h |  14 +-
 kernel/locking/lockdep_proc.c      |  31 ++-
 3 files changed, 312 insertions(+), 65 deletions(-)

-- 
2.18.1