On Mon, Feb 03, 2025 at 02:59:26PM +0100, Sebastian Andrzej Siewior wrote:
> The hashing of the private is slightly different and will be needed
> again while moving a futex_q entry to a different hash bucket after the
> resize.
>
> Move the private hashing into its own function.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/futex/core.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/futex/core.c b/kernel/futex/core.c
> index f608cd6ccc032..fdfc3402278a1 100644
> --- a/kernel/futex/core.c
> +++ b/kernel/futex/core.c
> @@ -117,6 +117,18 @@ static inline bool futex_key_is_private(union futex_key *key)
> return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED));
> }
>
> +static struct futex_hash_bucket *futex_hash_private(union futex_key *key,
> + struct futex_hash_bucket *fhb,
> + u32 hash_mask)
> +{
> + u32 hash;
> +
> + hash = jhash2((void *)&key->private.address,
> + sizeof(key->private.address) / 4,
> + key->both.offset);
> + return &fhb[hash & hash_mask];
> +}
> +
> /**
> * futex_hash - Return the hash bucket in the global or local hash
> * @key: Pointer to the futex key for which the hash is calculated
> @@ -131,14 +143,9 @@ struct futex_hash_bucket *futex_hash(union futex_key *key)
> u32 hash;
>
> fhb = current->mm->futex_hash_bucket;
> - if (fhb && futex_key_is_private(key)) {
> - u32 hash_mask = current->mm->futex_hash_mask;
> + if (fhb && futex_key_is_private(key))
> + return futex_hash_private(key, fhb, current->mm->futex_hash_mask);
>
> - hash = jhash2((void *)&key->private.address,
> - sizeof(key->private.address) / 4,
> - key->both.offset);
> - return &fhb[hash & hash_mask];
> - }
> hash = jhash2((u32 *)key,
> offsetof(typeof(*key), both.offset) / 4,
> key->both.offset);
Humph, this is a lot of back and forth. Maybe just do it right once?
Anyway, perhaps write it like:
static struct futex_hash_bucket *futex_hash_private(union futex_key *key)
{
struct mm_struct *mm;
u32 hash;
if (!futex_key_is_private(key))
return NULL;
mm = key->private.mm;
if (!mm->futex_hash_bucket)
return NULL;
/*
* Since key->private.mm is the same for all keys in this hash
* table, it does not contribute anything, and skipping it
* allows jhash2() to take a shorter/faster path.
*/
hash = jhash2((void *)&key->private.address,
sizeof(key->private.address) / 4,
key->both.offset);
return mm->futex_hash_bucket[hash & mm->futex_hash_mask];
}
struct futex_hash_bucket *futex_hash(union futex_key *key)
{
struct futex_hash_bucket *fhb;
u32 hash;
fhb = futex_hash_private(key);
if (fhb)
return fhb;
hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
key->both.offset);
return &futex_queues[hash & (futex_hashsize - 1)];
}