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    SubjectRe: [PATCH v5 6/7] locking/lockdep: Reuse freed chain_hlocks entries
    On Mon, Feb 03, 2020 at 11:41:46AM -0500, Waiman Long wrote:
    > + if (unlikely(size < 2))
    > + return; // XXX leak!

    Stuck this on top...

    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -2631,7 +2631,8 @@ struct lock_chain lock_chains[MAX_LOCKDE
    static DECLARE_BITMAP(lock_chains_in_use, MAX_LOCKDEP_CHAINS);
    static u16 chain_hlocks[MAX_LOCKDEP_CHAIN_HLOCKS];
    unsigned long nr_zapped_lock_chains;
    -unsigned int nr_free_chain_hlocks; /* Free cfhain_hlocks in buckets */
    +unsigned int nr_free_chain_hlocks; /* Free chain_hlocks in buckets */
    +unsigned int nr_lost_chain_hlocks; /* Lost chain_hlocks */
    unsigned int nr_large_chain_blocks; /* size > MAX_CHAIN_BUCKETS */

    /*
    @@ -2718,8 +2719,17 @@ static inline void add_chain_block(int o
    int bucket = size_to_bucket(size);
    int next = chain_block_buckets[bucket];

    - if (unlikely(size < 2))
    - return; // XXX leak!
    + if (unlikely(size < 2)) {
    + /*
    + * We can't store single entries on the freelist. Leak them.
    + *
    + * One possible way out would be to uniquely mark them, other
    + * than with CHAIN_BLK_FLAG, such that we can recover them when
    + * the block before it is re-added.
    + */
    + nr_lost_chain_hlocks++;
    + return;
    + }

    init_chain_block(offset, next, bucket, size);
    chain_block_buckets[bucket] = offset;
    @@ -2798,8 +2808,8 @@ static int alloc_chain_hlocks(int req)

    search:
    /*
    - * linear search in the 'dump' bucket; look for an exact match or the
    - * largest block.
    + * linear search of the variable sized freelist; look for an exact
    + * match or the largest block.
    */
    for_each_chain_block(0, prev, curr, next) {
    size = chain_block_size(curr);
    --- a/kernel/locking/lockdep_internals.h
    +++ b/kernel/locking/lockdep_internals.h
    @@ -141,6 +141,7 @@ extern unsigned int nr_hardirq_chains;
    extern unsigned int nr_softirq_chains;
    extern unsigned int nr_process_chains;
    extern unsigned int nr_free_chain_hlocks;
    +extern unsigned int nr_lost_chain_hlocks;
    extern unsigned int nr_large_chain_blocks;

    extern unsigned int max_lockdep_depth;
    --- a/kernel/locking/lockdep_proc.c
    +++ b/kernel/locking/lockdep_proc.c
    @@ -278,9 +278,11 @@ static int lockdep_stats_show(struct seq
    #ifdef CONFIG_PROVE_LOCKING
    seq_printf(m, " dependency chains: %11lu [max: %lu]\n",
    lock_chain_count(), MAX_LOCKDEP_CHAINS);
    - seq_printf(m, " dependency chain hlocks: %11lu [max: %lu]\n",
    - MAX_LOCKDEP_CHAIN_HLOCKS - nr_free_chain_hlocks,
    + seq_printf(m, " dependency chain hlocks used: %11lu [max: %lu]\n",
    + MAX_LOCKDEP_CHAIN_HLOCKS - (nr_free_chain_hlocks - nr_lost_chain_hlocks),
    MAX_LOCKDEP_CHAIN_HLOCKS);
    + seq_printf(m, " dependency chain hlocks free: %11lu\n", nr_free_chain_hlocks);
    + seq_printf(m, " dependency chain hlocks lost: %11lu\n", nr_lost_chain_hlocks);
    #endif

    #ifdef CONFIG_TRACE_IRQFLAGS
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