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    Subject[tip:sched/core] sched: Debug nested sleeps
    Commit-ID:  8eb23b9f35aae413140d3fda766a98092c21e9b0
    Gitweb: http://git.kernel.org/tip/8eb23b9f35aae413140d3fda766a98092c21e9b0
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Wed, 24 Sep 2014 10:18:55 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Tue, 28 Oct 2014 10:56:52 +0100

    sched: Debug nested sleeps

    Validate we call might_sleep() with TASK_RUNNING, which catches places
    where we nest blocking primitives, eg. mutex usage in a wait loop.

    Since all blocking is arranged through task_struct::state, nesting
    this will cause the inner primitive to set TASK_RUNNING and the outer
    will thus not block.

    Another observed problem is calling a blocking function from
    schedule()->sched_submit_work()->blk_schedule_flush_plug() which will
    then destroy the task state for the actual __schedule() call that
    comes after it.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: tglx@linutronix.de
    Cc: ilya.dryomov@inktank.com
    Cc: umgwanakikbuti@gmail.com
    Cc: oleg@redhat.com
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Link: http://lkml.kernel.org/r/20140924082242.591637616@infradead.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    include/linux/sched.h | 46 ++++++++++++++++++++++++++++++++++++++++++++--
    kernel/sched/core.c | 13 +++++++++++++
    2 files changed, 57 insertions(+), 2 deletions(-)

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 320a977..4648e07 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -243,6 +243,43 @@ extern char ___assert_task_state[1 - 2*!!(
    ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
    (task->flags & PF_FROZEN) == 0)

    +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
    +
    +#define __set_task_state(tsk, state_value) \
    + do { \
    + (tsk)->task_state_change = _THIS_IP_; \
    + (tsk)->state = (state_value); \
    + } while (0)
    +#define set_task_state(tsk, state_value) \
    + do { \
    + (tsk)->task_state_change = _THIS_IP_; \
    + set_mb((tsk)->state, (state_value)); \
    + } while (0)
    +
    +/*
    + * set_current_state() includes a barrier so that the write of current->state
    + * is correctly serialised wrt the caller's subsequent test of whether to
    + * actually sleep:
    + *
    + * set_current_state(TASK_UNINTERRUPTIBLE);
    + * if (do_i_need_to_sleep())
    + * schedule();
    + *
    + * If the caller does not need such serialisation then use __set_current_state()
    + */
    +#define __set_current_state(state_value) \
    + do { \
    + current->task_state_change = _THIS_IP_; \
    + current->state = (state_value); \
    + } while (0)
    +#define set_current_state(state_value) \
    + do { \
    + current->task_state_change = _THIS_IP_; \
    + set_mb(current->state, (state_value)); \
    + } while (0)
    +
    +#else
    +
    #define __set_task_state(tsk, state_value) \
    do { (tsk)->state = (state_value); } while (0)
    #define set_task_state(tsk, state_value) \
    @@ -259,11 +296,13 @@ extern char ___assert_task_state[1 - 2*!!(
    *
    * If the caller does not need such serialisation then use __set_current_state()
    */
    -#define __set_current_state(state_value) \
    +#define __set_current_state(state_value) \
    do { current->state = (state_value); } while (0)
    -#define set_current_state(state_value) \
    +#define set_current_state(state_value) \
    set_mb(current->state, (state_value))

    +#endif
    +
    /* Task command name length */
    #define TASK_COMM_LEN 16

    @@ -1661,6 +1700,9 @@ struct task_struct {
    unsigned int sequential_io;
    unsigned int sequential_io_avg;
    #endif
    +#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
    + unsigned long task_state_change;
    +#endif
    };

    /* Future-safe accessor for struct task_struct's cpus_allowed. */
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 0456a55..5b4b96b 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -7298,6 +7298,19 @@ void __might_sleep(const char *file, int line, int preempt_offset)
    {
    static unsigned long prev_jiffy; /* ratelimiting */

    + /*
    + * Blocking primitives will set (and therefore destroy) current->state,
    + * since we will exit with TASK_RUNNING make sure we enter with it,
    + * otherwise we will destroy state.
    + */
    + if (WARN(current->state != TASK_RUNNING,
    + "do not call blocking ops when !TASK_RUNNING; "
    + "state=%lx set at [<%p>] %pS\n",
    + current->state,
    + (void *)current->task_state_change,
    + (void *)current->task_state_change))
    + __set_current_state(TASK_RUNNING);
    +
    rcu_sleep_check(); /* WARN_ON_ONCE() by default, no rate limit reqd. */
    if ((preempt_count_equals(preempt_offset) && !irqs_disabled() &&
    !is_idle_task(current)) ||

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