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    Subject[PATCH 09/11] locking/mutex: Initialize mutex_waiter::ww_ctx with poison when debugging
    Date
    From: Nicolai Hähnle <Nicolai.Haehnle@amd.com>

    Help catch cases where mutex_lock is used directly on w/w mutexes, which
    otherwise result in the w/w tasks reading uninitialized data.

    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Maarten Lankhorst <dev@mblankhorst.nl>
    Cc: Daniel Vetter <daniel@ffwll.ch>
    Cc: Chris Wilson <chris@chris-wilson.co.uk>
    Cc: dri-devel@lists.freedesktop.org
    Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
    ---
    include/linux/poison.h | 1 +
    kernel/locking/mutex.c | 4 ++++
    2 files changed, 5 insertions(+)

    diff --git a/include/linux/poison.h b/include/linux/poison.h
    index 51334ed..a395403 100644
    --- a/include/linux/poison.h
    +++ b/include/linux/poison.h
    @@ -80,6 +80,7 @@
    /********** kernel/mutexes **********/
    #define MUTEX_DEBUG_INIT 0x11
    #define MUTEX_DEBUG_FREE 0x22
    +#define MUTEX_POISON_WW_CTX ((void *) 0x500 + POISON_POINTER_DELTA)

    /********** lib/flex_array.c **********/
    #define FLEX_ARRAY_FREE 0x6c /* for use-after-free poisoning */
    diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
    index 1e4da21..ee84007 100644
    --- a/kernel/locking/mutex.c
    +++ b/kernel/locking/mutex.c
    @@ -783,6 +783,10 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
    if (!use_ww_ctx) {
    /* add waiting tasks to the end of the waitqueue (FIFO): */
    list_add_tail(&waiter.list, &lock->wait_list);
    +
    +#ifdef CONFIG_DEBUG_MUTEXES
    + waiter.ww_ctx = MUTEX_POISON_WW_CTX;
    +#endif
    } else {
    /* Add in stamp order, waking up waiters that must back off. */
    ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
    --
    2.7.4
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