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    Subject[PATCH v5 1/7] locking/lockdep: Decrement irq context counters when removing lock chain
    Date
    There are currently three counters to track the irq context of a lock
    chain - nr_hardirq_chains, nr_softirq_chains and nr_process_chains.
    They are incremented when a new lock chain is added, but they are
    not decremented when a lock chain is removed. That causes some of the
    statistic counts reported by /proc/lockdep_stats to be incorrect.

    Fix that by decrementing the right counter when a lock chain is removed.

    Since inc_chains() no longer accesses hardirq_context and softirq_context
    directly, it is moved out from the CONFIG_TRACE_IRQFLAGS conditional
    compilation block.

    Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
    Signed-off-by: Waiman Long <longman@redhat.com>
    ---
    kernel/locking/lockdep.c | 40 +++++++++++++++++-------------
    kernel/locking/lockdep_internals.h | 6 +++++
    2 files changed, 29 insertions(+), 17 deletions(-)

    diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
    index 32406ef0d6a2..35449f5b79fb 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -2298,18 +2298,6 @@ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev,
    return 0;
    }

    -static void inc_chains(void)
    -{
    - if (current->hardirq_context)
    - nr_hardirq_chains++;
    - else {
    - if (current->softirq_context)
    - nr_softirq_chains++;
    - else
    - nr_process_chains++;
    - }
    -}
    -
    #else

    static inline int check_irq_usage(struct task_struct *curr,
    @@ -2317,13 +2305,27 @@ static inline int check_irq_usage(struct task_struct *curr,
    {
    return 1;
    }
    +#endif /* CONFIG_TRACE_IRQFLAGS */

    -static inline void inc_chains(void)
    +static void inc_chains(int irq_context)
    {
    - nr_process_chains++;
    + if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
    + nr_hardirq_chains++;
    + else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
    + nr_softirq_chains++;
    + else
    + nr_process_chains++;
    }

    -#endif /* CONFIG_TRACE_IRQFLAGS */
    +static void dec_chains(int irq_context)
    +{
    + if (irq_context & LOCK_CHAIN_HARDIRQ_CONTEXT)
    + nr_hardirq_chains--;
    + else if (irq_context & LOCK_CHAIN_SOFTIRQ_CONTEXT)
    + nr_softirq_chains--;
    + else
    + nr_process_chains--;
    +}

    static void
    print_deadlock_scenario(struct held_lock *nxt, struct held_lock *prv)
    @@ -2843,7 +2845,7 @@ static inline int add_chain_cache(struct task_struct *curr,

    hlist_add_head_rcu(&chain->entry, hash_head);
    debug_atomic_inc(chain_lookup_misses);
    - inc_chains();
    + inc_chains(chain->irq_context);

    return 1;
    }
    @@ -3596,7 +3598,8 @@ mark_usage(struct task_struct *curr, struct held_lock *hlock, int check)

    static inline unsigned int task_irq_context(struct task_struct *task)
    {
    - return 2 * !!task->hardirq_context + !!task->softirq_context;
    + return LOCK_CHAIN_HARDIRQ_CONTEXT * !!task->hardirq_context +
    + LOCK_CHAIN_SOFTIRQ_CONTEXT * !!task->softirq_context;
    }

    static int separate_irq_context(struct task_struct *curr,
    @@ -4798,6 +4801,8 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
    return;
    /* Overwrite the chain key for concurrent RCU readers. */
    WRITE_ONCE(chain->chain_key, chain_key);
    + dec_chains(chain->irq_context);
    +
    /*
    * Note: calling hlist_del_rcu() from inside a
    * hlist_for_each_entry_rcu() loop is safe.
    @@ -4819,6 +4824,7 @@ static void remove_class_from_lock_chain(struct pending_free *pf,
    }
    *new_chain = *chain;
    hlist_add_head_rcu(&new_chain->entry, chainhashentry(chain_key));
    + inc_chains(new_chain->irq_context);
    #endif
    }

    diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
    index 18d85aebbb57..a525368b8cf6 100644
    --- a/kernel/locking/lockdep_internals.h
    +++ b/kernel/locking/lockdep_internals.h
    @@ -106,6 +106,12 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
    #define STACK_TRACE_HASH_SIZE 16384
    #endif

    +/*
    + * Bit definitions for lock_chain.irq_context
    + */
    +#define LOCK_CHAIN_SOFTIRQ_CONTEXT (1 << 0)
    +#define LOCK_CHAIN_HARDIRQ_CONTEXT (1 << 1)
    +
    #define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)

    #define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
    --
    2.18.1
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