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    Subject[tip:core/locking] lockdep, kmemcheck: Annotate ->lock in lockdep_init_map()
    Commit-ID:  d3d03d4fc5b1bec3a579112de170a9676e9d97cb
    Gitweb: http://git.kernel.org/tip/d3d03d4fc5b1bec3a579112de170a9676e9d97cb
    Author: Yong Zhang <yong.zhang0@gmail.com>
    AuthorDate: Wed, 9 Nov 2011 16:04:51 +0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Tue, 6 Dec 2011 08:16:51 +0100

    lockdep, kmemcheck: Annotate ->lock in lockdep_init_map()

    Since commit f59de89 ("lockdep: Clear whole lockdep_map on initialization"),
    lockdep_init_map() will clear all the struct. But it will break
    lock_set_class()/lock_set_subclass(). A typical race condition
    is like below:

    CPU A CPU B
    lock_set_subclass(lockA);
    lock_set_class(lockA);
    lockdep_init_map(lockA);
    /* lockA->name is cleared */
    memset(lockA);
    __lock_acquire(lockA);
    /* lockA->class_cache[] is cleared */
    register_lock_class(lockA);
    look_up_lock_class(lockA);
    WARN_ON_ONCE(class->name !=
    lock->name);

    lock->name = name;

    So restore to what we have done before commit f59de89 but annotate
    ->lock with kmemcheck_mark_initialized() to suppress the kmemcheck
    warning reported in commit f59de89.

    Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Reported-by: Borislav Petkov <bp@alien8.de>
    Suggested-by: Vegard Nossum <vegard.nossum@gmail.com>
    Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: David Rientjes <rientjes@google.com>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Link: http://lkml.kernel.org/r/20111109080451.GB8124@zhy
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/lockdep.c | 8 +++++++-
    1 files changed, 7 insertions(+), 1 deletions(-)

    diff --git a/kernel/lockdep.c b/kernel/lockdep.c
    index a2ab30c..54cc0dc 100644
    --- a/kernel/lockdep.c
    +++ b/kernel/lockdep.c
    @@ -44,6 +44,7 @@
    #include <linux/stringify.h>
    #include <linux/bitops.h>
    #include <linux/gfp.h>
    +#include <linux/kmemcheck.h>

    #include <asm/sections.h>

    @@ -2950,7 +2951,12 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this,
    void lockdep_init_map(struct lockdep_map *lock, const char *name,
    struct lock_class_key *key, int subclass)
    {
    - memset(lock, 0, sizeof(*lock));
    + int i;
    +
    + kmemcheck_mark_initialized(lock, sizeof(*lock));
    +
    + for (i = 0; i < NR_LOCKDEP_CACHING_CLASSES; i++)
    + lock->class_cache[i] = NULL;

    #ifdef CONFIG_LOCK_STAT
    lock->cpu = raw_smp_processor_id();

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