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    Subject[PATCH] [42/99] lockdep: Fix lock_is_held() on recursion
    Date
    2.6.35-longterm review patch.  If anyone has any objections, please let me know.

    ------------------
    From: Peter Zijlstra <a.p.zijlstra@chello.nl>

    commit f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d upstream.

    The main lock_is_held() user is lockdep_assert_held(), avoid false
    assertions in lockdep_off() sections by unconditionally reporting the
    lock is taken.

    [ the reason this is important is a lockdep_assert_held() in ttwu()
    which triggers a warning under lockdep_off() as in printk() which
    can trigger another wakeup and lock up due to spinlock
    recursion, as reported and heroically debugged by Arne Jansen ]

    Reported-and-tested-by: Arne Jansen <lists@die-jansens.de>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Andi Kleen <ak@linux.intel.com>
    Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/lockdep.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    Index: linux-2.6.35.y/kernel/lockdep.c
    ===================================================================
    --- linux-2.6.35.y.orig/kernel/lockdep.c
    +++ linux-2.6.35.y/kernel/lockdep.c
    @@ -3250,7 +3250,7 @@ int lock_is_held(struct lockdep_map *loc
    int ret = 0;

    if (unlikely(current->lockdep_recursion))
    - return ret;
    + return 1; /* avoid false negative lockdep_assert_held() */

    raw_local_irq_save(flags);
    check_flags(flags);

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