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    Subject[PATCH tip/core/rcu 04/28] rcu: Restore checks for blocking in RCU read-side critical sections
    Date
    Long ago, using TREE_RCU with PREEMPT would result in "scheduling
    while atomic" diagnostics if you blocked in an RCU read-side critical
    section. However, PREEMPT now implies TREE_PREEMPT_RCU, which defeats
    this diagnostic. This commit therefore adds a replacement diagnostic
    based on PROVE_RCU.

    Because rcu_lockdep_assert() and lockdep_rcu_dereference() are now being
    used for things that have nothing to do with rcu_dereference(), rename
    lockdep_rcu_dereference() to lockdep_rcu_suspicious() and add a third
    argument that is a string indicating what is suspicious. This third
    argument is passed in from a new third argument to rcu_lockdep_assert().
    Update all calls to rcu_lockdep_assert() to add an informative third
    argument.

    Finally, add a pair of rcu_lockdep_assert() calls from within
    rcu_note_context_switch(), one complaining if a context switch occurs
    in an RCU-bh read-side critical section and another complaining if a
    context switch occurs in an RCU-sched read-side critical section.
    These are present only if the PROVE_RCU kernel parameter is enabled.

    Again, you must enable PROVE_RCU to see these new diagnostics. But you
    are enabling PROVE_RCU to check out new RCU uses in any case, aren't you?

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    include/linux/lockdep.h | 2 +-
    include/linux/rcupdate.h | 28 ++++++++++++---
    kernel/lockdep.c | 84 +++++++++++++++++++++++++--------------------
    kernel/pid.c | 4 ++-
    kernel/sched.c | 2 +
    5 files changed, 75 insertions(+), 45 deletions(-)

    diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
    index 4aef1dd..bfa66e7 100644
    --- a/include/linux/lockdep.h
    +++ b/include/linux/lockdep.h
    @@ -545,7 +545,7 @@ do { \
    #endif

    #ifdef CONFIG_PROVE_RCU
    -extern void lockdep_rcu_dereference(const char *file, const int line);
    +void lockdep_rcu_suspicious(const char *file, const int line, const char *s);
    #endif

    #endif /* __LINUX_LOCKDEP_H */
    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 99f9aa7..8be0433 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -297,19 +297,31 @@ extern int rcu_my_thread_group_empty(void);
    /**
    * rcu_lockdep_assert - emit lockdep splat if specified condition not met
    * @c: condition to check
    + * @s: informative message
    */
    -#define rcu_lockdep_assert(c) \
    +#define rcu_lockdep_assert(c, s) \
    do { \
    static bool __warned; \
    if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
    __warned = true; \
    - lockdep_rcu_dereference(__FILE__, __LINE__); \
    + lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
    } \
    } while (0)

    +#define rcu_sleep_check() \
    + do { \
    + rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
    + "Illegal context switch in RCU-bh" \
    + " read-side critical section"); \
    + rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
    + "Illegal context switch in RCU-sched"\
    + " read-side critical section"); \
    + } while (0)
    +
    #else /* #ifdef CONFIG_PROVE_RCU */

    -#define rcu_lockdep_assert(c) do { } while (0)
    +#define rcu_lockdep_assert(c, s) do { } while (0)
    +#define rcu_sleep_check() do { } while (0)

    #endif /* #else #ifdef CONFIG_PROVE_RCU */

    @@ -338,14 +350,16 @@ extern int rcu_my_thread_group_empty(void);
    #define __rcu_dereference_check(p, c, space) \
    ({ \
    typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
    - rcu_lockdep_assert(c); \
    + rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
    + " usage"); \
    rcu_dereference_sparse(p, space); \
    smp_read_barrier_depends(); \
    ((typeof(*p) __force __kernel *)(_________p1)); \
    })
    #define __rcu_dereference_protected(p, c, space) \
    ({ \
    - rcu_lockdep_assert(c); \
    + rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
    + " usage"); \
    rcu_dereference_sparse(p, space); \
    ((typeof(*p) __force __kernel *)(p)); \
    })
    @@ -359,7 +373,9 @@ extern int rcu_my_thread_group_empty(void);
    #define __rcu_dereference_index_check(p, c) \
    ({ \
    typeof(p) _________p1 = ACCESS_ONCE(p); \
    - rcu_lockdep_assert(c); \
    + rcu_lockdep_assert(c, \
    + "suspicious rcu_dereference_index_check()" \
    + " usage"); \
    smp_read_barrier_depends(); \
    (_________p1); \
    })
    diff --git a/kernel/lockdep.c b/kernel/lockdep.c
    index 53a6895..dbf453d 100644
    --- a/kernel/lockdep.c
    +++ b/kernel/lockdep.c
    @@ -1067,10 +1067,11 @@ print_circular_bug_header(struct lock_list *entry, unsigned int depth,
    if (debug_locks_silent)
    return 0;

    - printk("\n=======================================================\n");
    - printk( "[ INFO: possible circular locking dependency detected ]\n");
    + printk("\n");
    + printk("======================================================\n");
    + printk("[ INFO: possible circular locking dependency detected ]\n");
    print_kernel_version();
    - printk( "-------------------------------------------------------\n");
    + printk("-------------------------------------------------------\n");
    printk("%s/%d is trying to acquire lock:\n",
    curr->comm, task_pid_nr(curr));
    print_lock(check_src);
    @@ -1340,11 +1341,12 @@ print_bad_irq_dependency(struct task_struct *curr,
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
    return 0;

    - printk("\n======================================================\n");
    - printk( "[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
    + printk("\n");
    + printk("======================================================\n");
    + printk("[ INFO: %s-safe -> %s-unsafe lock order detected ]\n",
    irqclass, irqclass);
    print_kernel_version();
    - printk( "------------------------------------------------------\n");
    + printk("------------------------------------------------------\n");
    printk("%s/%d [HC%u[%lu]:SC%u[%lu]:HE%u:SE%u] is trying to acquire:\n",
    curr->comm, task_pid_nr(curr),
    curr->hardirq_context, hardirq_count() >> HARDIRQ_SHIFT,
    @@ -1546,10 +1548,11 @@ print_deadlock_bug(struct task_struct *curr, struct held_lock *prev,
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
    return 0;

    - printk("\n=============================================\n");
    - printk( "[ INFO: possible recursive locking detected ]\n");
    + printk("\n");
    + printk("=============================================\n");
    + printk("[ INFO: possible recursive locking detected ]\n");
    print_kernel_version();
    - printk( "---------------------------------------------\n");
    + printk("---------------------------------------------\n");
    printk("%s/%d is trying to acquire lock:\n",
    curr->comm, task_pid_nr(curr));
    print_lock(next);
    @@ -2018,10 +2021,11 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
    return 0;

    - printk("\n=================================\n");
    - printk( "[ INFO: inconsistent lock state ]\n");
    + printk("\n");
    + printk("=================================\n");
    + printk("[ INFO: inconsistent lock state ]\n");
    print_kernel_version();
    - printk( "---------------------------------\n");
    + printk("---------------------------------\n");

    printk("inconsistent {%s} -> {%s} usage.\n",
    usage_str[prev_bit], usage_str[new_bit]);
    @@ -2076,10 +2080,11 @@ print_irq_inversion_bug(struct task_struct *curr,
    if (!debug_locks_off_graph_unlock() || debug_locks_silent)
    return 0;

    - printk("\n=========================================================\n");
    - printk( "[ INFO: possible irq lock inversion dependency detected ]\n");
    + printk("\n");
    + printk("=========================================================\n");
    + printk("[ INFO: possible irq lock inversion dependency detected ]\n");
    print_kernel_version();
    - printk( "---------------------------------------------------------\n");
    + printk("---------------------------------------------------------\n");
    printk("%s/%d just changed the state of lock:\n",
    curr->comm, task_pid_nr(curr));
    print_lock(this);
    @@ -2869,9 +2874,10 @@ print_unlock_inbalance_bug(struct task_struct *curr, struct lockdep_map *lock,
    if (debug_locks_silent)
    return 0;

    - printk("\n=====================================\n");
    - printk( "[ BUG: bad unlock balance detected! ]\n");
    - printk( "-------------------------------------\n");
    + printk("\n");
    + printk("=====================================\n");
    + printk("[ BUG: bad unlock balance detected! ]\n");
    + printk("-------------------------------------\n");
    printk("%s/%d is trying to release lock (",
    curr->comm, task_pid_nr(curr));
    print_lockdep_cache(lock);
    @@ -3276,9 +3282,10 @@ print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
    if (debug_locks_silent)
    return 0;

    - printk("\n=================================\n");
    - printk( "[ BUG: bad contention detected! ]\n");
    - printk( "---------------------------------\n");
    + printk("\n");
    + printk("=================================\n");
    + printk("[ BUG: bad contention detected! ]\n");
    + printk("---------------------------------\n");
    printk("%s/%d is trying to contend lock (",
    curr->comm, task_pid_nr(curr));
    print_lockdep_cache(lock);
    @@ -3637,9 +3644,10 @@ print_freed_lock_bug(struct task_struct *curr, const void *mem_from,
    if (debug_locks_silent)
    return;

    - printk("\n=========================\n");
    - printk( "[ BUG: held lock freed! ]\n");
    - printk( "-------------------------\n");
    + printk("\n");
    + printk("=========================\n");
    + printk("[ BUG: held lock freed! ]\n");
    + printk("-------------------------\n");
    printk("%s/%d is freeing memory %p-%p, with a lock still held there!\n",
    curr->comm, task_pid_nr(curr), mem_from, mem_to-1);
    print_lock(hlock);
    @@ -3693,9 +3701,10 @@ static void print_held_locks_bug(struct task_struct *curr)
    if (debug_locks_silent)
    return;

    - printk("\n=====================================\n");
    - printk( "[ BUG: lock held at task exit time! ]\n");
    - printk( "-------------------------------------\n");
    + printk("\n");
    + printk("=====================================\n");
    + printk("[ BUG: lock held at task exit time! ]\n");
    + printk("-------------------------------------\n");
    printk("%s/%d is exiting with locks still held!\n",
    curr->comm, task_pid_nr(curr));
    lockdep_print_held_locks(curr);
    @@ -3789,16 +3798,17 @@ void lockdep_sys_exit(void)
    if (unlikely(curr->lockdep_depth)) {
    if (!debug_locks_off())
    return;
    - printk("\n================================================\n");
    - printk( "[ BUG: lock held when returning to user space! ]\n");
    - printk( "------------------------------------------------\n");
    + printk("\n");
    + printk("================================================\n");
    + printk("[ BUG: lock held when returning to user space! ]\n");
    + printk("------------------------------------------------\n");
    printk("%s/%d is leaving the kernel with locks still held!\n",
    curr->comm, curr->pid);
    lockdep_print_held_locks(curr);
    }
    }

    -void lockdep_rcu_dereference(const char *file, const int line)
    +void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
    {
    struct task_struct *curr = current;

    @@ -3807,15 +3817,15 @@ void lockdep_rcu_dereference(const char *file, const int line)
    return;
    #endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
    /* Note: the following can be executed concurrently, so be careful. */
    - printk("\n===================================================\n");
    - printk( "[ INFO: suspicious rcu_dereference_check() usage. ]\n");
    - printk( "---------------------------------------------------\n");
    - printk("%s:%d invoked rcu_dereference_check() without protection!\n",
    - file, line);
    + printk("\n");
    + printk("===============================\n");
    + printk("[ INFO: suspicious RCU usage. ]\n");
    + printk("-------------------------------\n");
    + printk("%s:%d %s!\n", file, line, s);
    printk("\nother info that might help us debug this:\n\n");
    printk("\nrcu_scheduler_active = %d, debug_locks = %d\n", rcu_scheduler_active, debug_locks);
    lockdep_print_held_locks(curr);
    printk("\nstack backtrace:\n");
    dump_stack();
    }
    -EXPORT_SYMBOL_GPL(lockdep_rcu_dereference);
    +EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);
    diff --git a/kernel/pid.c b/kernel/pid.c
    index 57a8346..a7577b3 100644
    --- a/kernel/pid.c
    +++ b/kernel/pid.c
    @@ -419,7 +419,9 @@ EXPORT_SYMBOL(pid_task);
    */
    struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
    {
    - rcu_lockdep_assert(rcu_read_lock_held());
    + rcu_lockdep_assert(rcu_read_lock_held(),
    + "find_task_by_pid_ns() needs rcu_read_lock()"
    + " protection");
    return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
    }

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 312f8b9..1352dbb 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -4021,6 +4021,7 @@ static inline void schedule_debug(struct task_struct *prev)
    */
    if (unlikely(in_atomic_preempt_off() && !prev->exit_state))
    __schedule_bug(prev);
    + rcu_sleep_check();

    profile_hit(SCHED_PROFILING, __builtin_return_address(0));

    @@ -8309,6 +8310,7 @@ void __might_sleep(const char *file, int line, int preempt_offset)
    #ifdef in_atomic
    static unsigned long prev_jiffy; /* ratelimiting */

    + rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
    if ((preempt_count_equals(preempt_offset) && !irqs_disabled()) ||
    system_state != SYSTEM_RUNNING || oops_in_progress)
    return;
    --
    1.7.3.2


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