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    Subject[PATCH v4 1/2] lib/vsprintf: Remove static_branch_likely() from __ptr_to_hashval().
    Date
    Using static_branch_likely() to signal that ptr_key has been filled is a
    bit much given that it is not a fast path.

    Replace static_branch_likely() with bool for condition and a memory
    barrier for ptr_key.

    Suggested-by: Petr Mladek <pmladek@suse.com>
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    ---
    lib/vsprintf.c | 19 ++++++++-----------
    1 file changed, 8 insertions(+), 11 deletions(-)

    diff --git a/lib/vsprintf.c b/lib/vsprintf.c
    index 3c1853a9d1c09..bce63cbf23779 100644
    --- a/lib/vsprintf.c
    +++ b/lib/vsprintf.c
    @@ -750,12 +750,7 @@ static int __init debug_boot_weak_hash_enable(char *str)
    }
    early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable);

    -static DEFINE_STATIC_KEY_FALSE(filled_random_ptr_key);
    -
    -static void enable_ptr_key_workfn(struct work_struct *work)
    -{
    - static_branch_enable(&filled_random_ptr_key);
    -}
    +static bool filled_random_ptr_key __read_mostly;

    /* Maps a pointer to a 32 bit unique identifier. */
    static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
    @@ -763,24 +758,26 @@ static inline int __ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
    static siphash_key_t ptr_key __read_mostly;
    unsigned long hashval;

    - if (!static_branch_likely(&filled_random_ptr_key)) {
    + if (!READ_ONCE(filled_random_ptr_key)) {
    static bool filled = false;
    static DEFINE_SPINLOCK(filling);
    - static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
    unsigned long flags;

    - if (!system_unbound_wq || !rng_is_initialized() ||
    + if (!rng_is_initialized() ||
    !spin_trylock_irqsave(&filling, flags))
    return -EAGAIN;

    if (!filled) {
    get_random_bytes(&ptr_key, sizeof(ptr_key));
    - queue_work(system_unbound_wq, &enable_ptr_key_work);
    + /* Pairs with smp_rmb() before reading ptr_key. */
    + smp_wmb();
    + WRITE_ONCE(filled_random_ptr_key, true);
    filled = true;
    }
    spin_unlock_irqrestore(&filling, flags);
    }
    -
    + /* Pairs with smp_wmb() after writing ptr_key. */
    + smp_rmb();

    #ifdef CONFIG_64BIT
    hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
    --
    2.37.2
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