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    SubjectRe: processes hung after sys_renameat, and 'missing' processes
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    Date
    On Fri, 2012-06-08 at 11:01 -0400, Dave Jones wrote:
    > gaah, it's quoted-printable damaged. When I save that in mutt, I get a
    > file that contains crap like

    ok, evolution is no longer able to send plain text.. git can deal with
    quoted printable, and I have an awk script to decipher it. Still bloody
    annoying though.

    Attached now :/


    Subject: Re: processes hung after sys_renameat, and 'missing' processes
    From: Peter Zijlstra <peterz@infradead.org>
    Date: Fri, 08 Jun 2012 09:31:38 +0200

    On Thu, 2012-06-07 at 08:30 -0700, Linus Torvalds wrote:
    > On Thu, Jun 7, 2012 at 3:26 AM, Peter Zijlstra <peterz@infradead.org> wro=
    te:
    > > On Wed, 2012-06-06 at 16:31 -0700, Linus Torvalds wrote:
    > >> PeterZ - the fact that we use mutex_lock_nested with
    > >> I_MUTEX_PARENT/I_MUTEX_CHILD/nothing hopefully doesn't screw us up in
    > >> case we get it wrong, right?
    > >
    > > Sadly, if you get that annotation wrong you can annotate an actual
    > > deadlock away. This the reason you have to be very careful when
    > > annotating stuff.
    >=20
    > Is that true even if you can see an actual deadlock on the lock *instance=
    s*?

    Yep.. :/

    > The point of the locking classes (to me) was always that you could see
    > the deadlock even if it didn't *actually* happen, just *potentially*
    > happened. If the lock classes then mean that that hides an actual
    > deadlock information, that's a big downside.

    Right, so in order to report a deadlock on instances we'd have to do a
    full lock graph walk on every contended lock acquisition. This is quite
    expensive.

    Although I can look into doing that from say the NMI watchdog and/or
    some sysrq key.

    > And yeah, that really means that we absolutely *have* to get the
    > instance data in the lock debug printout, since we can't see deadlocks
    > any other way.=20

    Well, typically deadlocks aren't that hard to find once you trigger
    them. The current case of course being the exception to that rule..=20

    > Can you check the compile error that Dave reported for
    > your patch, because right now Dave is running without it, afaik, due
    > to your lock-instance patch not really working in practice.

    Oh, missed that in the thread.. yeah here goes.


    Now also compile tested with CONFIG_LOCK_STAT...

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/1339140698.23343.26.camel@twins
    ---
    include/linux/lockdep.h | 44 ++++++++-------
    include/trace/events/lock.h | 3 -
    kernel/lockdep.c | 128 ++++++++++++++++++++++++++++----------------
    3 files changed, 107 insertions(+), 68 deletions(-)

    --- a/include/linux/lockdep.h
    +++ b/include/linux/lockdep.h
    @@ -211,6 +211,13 @@ struct lock_chain {
    */
    #define MAX_LOCKDEP_KEYS ((1UL << MAX_LOCKDEP_KEYS_BITS) - 1)

    +enum held_lock_state {
    + hls_unheld = 0,
    + hls_acquiring,
    + hls_contended,
    + hls_acquired,
    +};
    +
    struct held_lock {
    /*
    * One-way hash of the dependency chain up to this point. We
    @@ -254,7 +261,10 @@ struct held_lock {
    unsigned int read:2; /* see lock_acquire() comment */
    unsigned int check:2; /* see lock_acquire() comment */
    unsigned int hardirqs_off:1;
    - unsigned int references:11; /* 32 bits */
    + unsigned int state:2; /* see held_lock_state */
    + /* 9 bit hole */
    + unsigned int references:16;
    + /* 16 bit hole */
    };

    /*
    @@ -363,6 +373,18 @@ extern void lockdep_trace_alloc(gfp_t ma

    #define lockdep_recursing(tsk) ((tsk)->lockdep_recursion)

    +extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
    +extern void lock_acquired(struct lockdep_map *lock, unsigned long ip);
    +
    +#define LOCK_CONTENDED(_lock, try, lock) \
    +do { \
    + if (!try(_lock)) { \
    + lock_contended(&(_lock)->dep_map, _RET_IP_); \
    + lock(_lock); \
    + } \
    + lock_acquired(&(_lock)->dep_map, _RET_IP_); \
    +} while (0)
    +
    #else /* !LOCKDEP */

    static inline void lockdep_off(void)
    @@ -414,31 +436,13 @@ struct lock_class_key { };

    #define lockdep_recursing(tsk) (0)

    -#endif /* !LOCKDEP */
    -
    -#ifdef CONFIG_LOCK_STAT
    -
    -extern void lock_contended(struct lockdep_map *lock, unsigned long ip);
    -extern void lock_acquired(struct lockdep_map *lock, unsigned long ip);
    -
    -#define LOCK_CONTENDED(_lock, try, lock) \
    -do { \
    - if (!try(_lock)) { \
    - lock_contended(&(_lock)->dep_map, _RET_IP_); \
    - lock(_lock); \
    - } \
    - lock_acquired(&(_lock)->dep_map, _RET_IP_); \
    -} while (0)
    -
    -#else /* CONFIG_LOCK_STAT */
    -
    #define lock_contended(lockdep_map, ip) do {} while (0)
    #define lock_acquired(lockdep_map, ip) do {} while (0)

    #define LOCK_CONTENDED(_lock, try, lock) \
    lock(_lock)

    -#endif /* CONFIG_LOCK_STAT */
    +#endif /* !LOCKDEP */

    #ifdef CONFIG_LOCKDEP

    --- a/include/trace/events/lock.h
    +++ b/include/trace/events/lock.h
    @@ -61,8 +61,6 @@ DEFINE_EVENT(lock, lock_release,
    TP_ARGS(lock, ip)
    );

    -#ifdef CONFIG_LOCK_STAT
    -
    DEFINE_EVENT(lock, lock_contended,

    TP_PROTO(struct lockdep_map *lock, unsigned long ip),
    @@ -78,7 +76,6 @@ DEFINE_EVENT(lock, lock_acquired,
    );

    #endif
    -#endif

    #endif /* _TRACE_LOCK_H */

    --- a/kernel/lockdep.c
    +++ b/kernel/lockdep.c
    @@ -541,10 +541,23 @@ static void print_lockdep_cache(struct l
    printk("%s", name);
    }

    +static void print_lock_state(struct held_lock *hlock)
    +{
    + switch (hlock->state) {
    + /* holding an unheld lock is fail! */
    + case hls_unheld: printk("FAIL: "); break;
    +
    + case hls_acquiring: /* fall-through */
    + case hls_contended: printk("blocked: "); break;
    + case hls_acquired: printk("held: "); break;
    + };
    +}
    +
    static void print_lock(struct held_lock *hlock)
    {
    + print_lock_state(hlock);
    print_lock_name(hlock_class(hlock));
    - printk(", at: ");
    + printk(", instance: %p, at: ", hlock->instance);
    print_ip_sym(hlock->acquire_ip);
    }

    @@ -556,7 +569,7 @@ static void lockdep_print_held_locks(str
    printk("no locks held by %s/%d.\n", curr->comm, task_pid_nr(curr));
    return;
    }
    - printk("%d lock%s held by %s/%d:\n",
    + printk("%d lock%s on stack by %s/%d:\n",
    depth, depth > 1 ? "s" : "", curr->comm, task_pid_nr(curr));

    for (i = 0; i < depth; i++) {
    @@ -3093,6 +3106,7 @@ static int __lock_acquire(struct lockdep
    hlock->check = check;
    hlock->hardirqs_off = !!hardirqs_off;
    hlock->references = references;
    + hlock->state = hls_acquiring;
    #ifdef CONFIG_LOCK_STAT
    hlock->waittime_stamp = 0;
    hlock->holdtime_stamp = lockstat_clock();
    @@ -3607,7 +3621,6 @@ void lockdep_clear_current_reclaim_state
    current->lockdep_reclaim_gfp = 0;
    }

    -#ifdef CONFIG_LOCK_STAT
    static int
    print_lock_contention_bug(struct task_struct *curr, struct lockdep_map *lock,
    unsigned long ip)
    @@ -3637,14 +3650,73 @@ print_lock_contention_bug(struct task_st
    return 0;
    }

    +#ifdef CONFIG_LOCK_STAT
    +
    +static void lockstat_contended(struct held_lock *hlock, unsigned long ip)
    +{
    + struct lockdep_map *lock = hlock->instance;
    + int contention_point, contending_point;
    + struct lock_class_stats *stats;
    +
    + hlock->waittime_stamp = lockstat_clock();
    +
    + contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
    + contending_point = lock_point(hlock_class(hlock)->contending_point,
    + lock->ip);
    +
    + stats = get_lock_stats(hlock_class(hlock));
    + if (contention_point < LOCKSTAT_POINTS)
    + stats->contention_point[contention_point]++;
    + if (contending_point < LOCKSTAT_POINTS)
    + stats->contending_point[contending_point]++;
    + if (lock->cpu != smp_processor_id())
    + stats->bounces[bounce_contended + !!hlock->read]++;
    + put_lock_stats(stats);
    +}
    +
    +static void lockstat_acquired(struct held_lock *hlock, unsigned long ip)
    +{
    + struct lockdep_map *lock = hlock->instance;
    + struct lock_class_stats *stats;
    + u64 now, waittime = 0;
    + int cpu;
    +
    + cpu = smp_processor_id();
    + if (hlock->waittime_stamp) {
    + now = lockstat_clock();
    + waittime = now - hlock->waittime_stamp;
    + hlock->holdtime_stamp = now;
    + }
    +
    + stats = get_lock_stats(hlock_class(hlock));
    + if (waittime) {
    + if (hlock->read)
    + lock_time_inc(&stats->read_waittime, waittime);
    + else
    + lock_time_inc(&stats->write_waittime, waittime);
    + }
    + if (lock->cpu != cpu)
    + stats->bounces[bounce_acquired + !!hlock->read]++;
    + put_lock_stats(stats);
    +
    + lock->cpu = cpu;
    + lock->ip = ip;
    +}
    +
    +#else /* CONFIG_LOCK_STAT */
    +
    +static inline void lockstat_contended(struct held_lock *hlock, unsigned long ip) { }
    +static inline void lockstat_acquired(struct held_lock *hlock, unsigned long ip) { }
    +
    +#endif /* CONFIG_LOCK_STAT */
    +
    static void
    __lock_contended(struct lockdep_map *lock, unsigned long ip)
    {
    struct task_struct *curr = current;
    struct held_lock *hlock, *prev_hlock;
    - struct lock_class_stats *stats;
    unsigned int depth;
    - int i, contention_point, contending_point;
    + int i;

    depth = curr->lockdep_depth;
    /*
    @@ -3673,20 +3745,8 @@ __lock_contended(struct lockdep_map *loc
    if (hlock->instance != lock)
    return;

    - hlock->waittime_stamp = lockstat_clock();
    -
    - contention_point = lock_point(hlock_class(hlock)->contention_point, ip);
    - contending_point = lock_point(hlock_class(hlock)->contending_point,
    - lock->ip);
    -
    - stats = get_lock_stats(hlock_class(hlock));
    - if (contention_point < LOCKSTAT_POINTS)
    - stats->contention_point[contention_point]++;
    - if (contending_point < LOCKSTAT_POINTS)
    - stats->contending_point[contending_point]++;
    - if (lock->cpu != smp_processor_id())
    - stats->bounces[bounce_contended + !!hlock->read]++;
    - put_lock_stats(stats);
    + hlock->state = hls_contended;
    + lockstat_contended(hlock, ip);
    }

    static void
    @@ -3694,10 +3754,8 @@ __lock_acquired(struct lockdep_map *lock
    {
    struct task_struct *curr = current;
    struct held_lock *hlock, *prev_hlock;
    - struct lock_class_stats *stats;
    unsigned int depth;
    - u64 now, waittime = 0;
    - int i, cpu;
    + int i;

    depth = curr->lockdep_depth;
    /*
    @@ -3726,28 +3784,8 @@ __lock_acquired(struct lockdep_map *lock
    if (hlock->instance != lock)
    return;

    - cpu = smp_processor_id();
    - if (hlock->waittime_stamp) {
    - now = lockstat_clock();
    - waittime = now - hlock->waittime_stamp;
    - hlock->holdtime_stamp = now;
    - }
    -
    - trace_lock_acquired(lock, ip);
    -
    - stats = get_lock_stats(hlock_class(hlock));
    - if (waittime) {
    - if (hlock->read)
    - lock_time_inc(&stats->read_waittime, waittime);
    - else
    - lock_time_inc(&stats->write_waittime, waittime);
    - }
    - if (lock->cpu != cpu)
    - stats->bounces[bounce_acquired + !!hlock->read]++;
    - put_lock_stats(stats);
    -
    - lock->cpu = cpu;
    - lock->ip = ip;
    + hlock->state = hls_acquired;
    + lockstat_acquired(hlock, ip);
    }

    void lock_contended(struct lockdep_map *lock, unsigned long ip)
    @@ -3783,12 +3821,12 @@ void lock_acquired(struct lockdep_map *l
    raw_local_irq_save(flags);
    check_flags(flags);
    current->lockdep_recursion = 1;
    + trace_lock_acquired(lock, ip);
    __lock_acquired(lock, ip);
    current->lockdep_recursion = 0;
    raw_local_irq_restore(flags);
    }
    EXPORT_SYMBOL_GPL(lock_acquired);
    -#endif

    /*
    * Used by the testsuite, sanitize the validator state
    \
     
     \ /
      Last update: 2012-06-08 17:41    [W:2.510 / U:0.312 seconds]
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