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    Subject[TIP][RFC 2/7] futex: futex_top_waiter()
    From: Darren Hart <dvhltc@us.ibm.com>

    Improve legibility by wrapping finding the top waiter in a function. This
    will be used by the follow-on patches for enabling requeue pi.

    Changelog:
    V4: -Simplified logic in the hb loop
    -Return the futex_q as the task can be had from there if needed
    -Updated comments and dropped the -safe iterator per review from tglx
    V3: -Comment linewidth cleanup
    V1: -Initial version

    Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
    ---

    kernel/futex.c | 26 ++++++++++++++++++++++++++
    1 files changed, 26 insertions(+), 0 deletions(-)


    diff --git a/kernel/futex.c b/kernel/futex.c
    index 16459c2..d02962b 100644
    --- a/kernel/futex.c
    +++ b/kernel/futex.c
    @@ -277,6 +277,32 @@ void put_futex_key(int fshared, union futex_key *key)
    drop_futex_key_refs(key);
    }

    +/*
    + * futex_top_waiter - return the highest priority waiter on the futex specified
    + * by key
    + * @hb: the hash bucket the futex_q's reside in
    + * @key: the futex key (to distinguish it from other futex futex_q's)
    + *
    + * Must be called with the hb lock held.
    + *
    + */
    +static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
    + union futex_key *key)
    +{
    + struct plist_head *head;
    + struct futex_q *this;
    + struct futex_q *top_waiter = NULL;
    +
    + head = &hb->chain;
    + plist_for_each_entry(this, head, list) {
    + if (match_futex(&this->key, key)) {
    + top_waiter = this;
    + break;
    + }
    + }
    + return top_waiter;
    +}
    +
    static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
    {
    u32 curval;
    --
    Darren Hart
    IBM Linux Technology Center
    Real-Time Linux Team

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