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    Subject[PATCH AUTOSEL 5.4 126/330] locking/lockdep: Decrement IRQ context counters when removing lock chain
    Date
    From: Waiman Long <longman@redhat.com>

    [ Upstream commit b3b9c187dc2544923a601733a85352b9ddaba9b3 ]

    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.
    IRQ
    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>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Link: https://lkml.kernel.org/r/20200206152408.24165-2-longman@redhat.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 9ab1a965c3b92..bca0f7f71cde4 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -2302,18 +2302,6 @@ 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,
    @@ -2321,13 +2309,27 @@ 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)
    @@ -2847,7 +2849,7 @@ 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;
    }
    @@ -3600,7 +3602,8 @@ lock_used:

    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,
    @@ -4805,6 +4808,8 @@ recalc:
    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.
    @@ -4826,6 +4831,7 @@ recalc:
    }
    *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 18d85aebbb57f..a525368b8cf61 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)
    --
    2.25.1
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