From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D020840861A for ; Wed, 10 Jun 2026 13:55:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781099730; cv=none; b=LUu6bT46u0Jk9ossblDXQvn8AEIxcs7CRA1WI3aceCc7K/meo/wxUPyFzugeQdbNbTkUloDkw4BrBdRWs0ok9jtOZJ/2udJsOrgLuR1/F5oeStLbrpgC7Gw5IqAvO0o2AVxNGsBCZlkN0HyhvpPZGnDW9Qx4LIBnPS0AC3o2mKQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781099730; c=relaxed/simple; bh=QnWeQ4rWuA/eMB0mYmMOJmqY7OfnTLwiGDQLo7rTWo8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=FHttFUX67YPcQ1taioJauqBw7uGcqisWReuRzbtAWyNtMHMc73dOKUiLif/YDA2wyJkkD6Jg0HVhXYuPIQn1QLZqHOdhosqmQoAOniRpssR3TJTXuaT3tv/mhSzLlKUBr0xINEhgb6C2sbzDeaRqsaYpAWituzSLCZFoYG5jhuw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=MjwA0TfA; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="MjwA0TfA" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4KJ8CS0khxEwphkaDuexADfx+7N/iHMnAjaZOqVh8yA=; b=MjwA0TfAaCC7+vAGnRv+n7f92z wRGNqOp5yHoRyPuW04Wpp/sxp5SdaAgnZx1RRnuMh1qb+6CV7auNqFGS71eUjESXBAXOti8QUgD4l aeIpplQs19gw58KdbHcRArQQgrMp7Kn8VAY2S58dlFQ+IqQsoFeRLD1qAUdpgYwMMRJxbI5LUf0ie HFNnENEwg1HrV2IZWSFu5iNxMn0PaGc1YA2QYx7l3i2T8SIiiBdxI9l0bbspXLvSRDdhXBj87s9P7 AtIH+ncb6VAFsULC1v9NB5xpeSrVMPd+b6Sc3xUa8fVltu6ozsx0zzep9TjNx1Zff5Q4xh3g/kkHp k0lLG74A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1wXJOi-00000003xZ1-0as2; Wed, 10 Jun 2026 13:55:12 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 772E530036F; Wed, 10 Jun 2026 15:55:10 +0200 (CEST) Date: Wed, 10 Jun 2026 15:55:10 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Breno Leitao , Ingo Molnar , Darren Hart , Davidlohr Bueso , =?iso-8859-1?Q?Andr=E9?= Almeida , linux-kernel@vger.kernel.org, puranjay@kernel.org, rmikey@meta.com, stuclar@meta.com, namhyung@kernel.org, kernel-team@meta.com Subject: Re: [PATCH RFC] futex: avoid false sharing between hb->chain and the bucket lock Message-ID: <20260610135510.GB1430057@noisy.programming.kicks-ass.net> References: <20260605-futex-v1-1-4ad4a0d6f265@debian.org> <20260609104603.GA48970@noisy.programming.kicks-ass.net> <20260609201117.GA187714@noisy.programming.kicks-ass.net> <20260609201809.GA1430057@noisy.programming.kicks-ass.net> <87h5na3ait.ffs@fw13> <20260610112546.GE187714@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260610112546.GE187714@noisy.programming.kicks-ass.net> On Wed, Jun 10, 2026 at 01:25:46PM +0200, Peter Zijlstra wrote: > On Wed, Jun 10, 2026 at 01:22:34PM +0200, Thomas Gleixner wrote: > > On Tue, Jun 09 2026 at 22:18, Peter Zijlstra wrote: > > > On Tue, Jun 09, 2026 at 10:11:17PM +0200, Peter Zijlstra wrote: > > >> Anyway, how does something like the below work for you? It's a total > > >> hack job, but it (sorta) builds and runs. > > >> > > > > > > Please use this one, I spotted a silly bug. > > > > So I ran this on two machines. > > > > SKL dual socket 112 threads: > > > > Baseline Patched > > > > shared (16k) 1571857 1641435 + 4.4% > > autosize (512) 646390 903371 +39.7% > > -b 256 464395 587014 +26.4% > > -b 512 715687 995943 +39.2% > > -b 1024 995085 1396328 +40.3% > > -b 2048 1293114 1668395 +29.0% > > -b 4096 2124438 2240228 + 5.5% > > > > Zen3 dual socket 256 threads: > > > > Baseline Patched > > > > shared (16k) 1275840 1381279 + 8.2% > > autosize (512) 1252745 1482179 +18.3% > > -b 256 856274 955455 +11.5% > > -b 512 1267490 1544010 +21.8% > > -b 1024 1424013 1625424 +14.1% > > -b 2048 1505181 1669342 +10.9% > > -b 4096 1465993 1688932 +15.2% > > I suppose that means I'd better go make it prettier and survive > randconfig :-) I ended up with the below. I'll invent a Changelog and throw it to the robots later tonight. --- kernel/futex/core.c | 108 +++++++++++++----------------------------------- kernel/futex/futex.h | 37 ++++++++++------- kernel/futex/pi.c | 21 +++++----- kernel/futex/requeue.c | 20 ++++----- kernel/futex/waitwake.c | 17 +++++--- 5 files changed, 84 insertions(+), 119 deletions(-) diff --git a/kernel/futex/core.c b/kernel/futex/core.c index ff2a4fb2993f..844fe893646f 100644 --- a/kernel/futex/core.c +++ b/kernel/futex/core.c @@ -124,7 +124,7 @@ late_initcall(fail_futex_debugfs); #endif /* CONFIG_FAIL_FUTEX */ static struct futex_hash_bucket * -__futex_hash(union futex_key *key, struct futex_private_hash *fph); +__futex_hash(union futex_key *key, struct futex_private_hash *fph, struct futex_private_hash **fph_p); #ifdef CONFIG_FUTEX_PRIVATE_HASH static bool futex_ref_get(struct futex_private_hash *fph); @@ -133,15 +133,6 @@ static bool futex_ref_is_dead(struct futex_private_hash *fph); enum { FR_PERCPU = 0, FR_ATOMIC }; -static inline bool futex_key_is_private(union futex_key *key) -{ - /* - * Relies on get_futex_key() to set either bit for shared - * futexes -- see comment with union futex_key. - */ - return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED)); -} - static bool futex_private_hash_get(struct futex_private_hash *fph) { return futex_ref_get(fph); @@ -149,48 +140,15 @@ static bool futex_private_hash_get(struct futex_private_hash *fph) void futex_private_hash_put(struct futex_private_hash *fph) { - if (futex_ref_put(fph)) + if (fph && futex_ref_put(fph)) wake_up_var(fph->mm); } -/** - * futex_hash_get - Get an additional reference for the local hash. - * @hb: ptr to the private local hash. - * - * Obtain an additional reference for the already obtained hash bucket. The - * caller must already own an reference. - */ -void futex_hash_get(struct futex_hash_bucket *hb) -{ - struct futex_private_hash *fph = hb->priv; - - if (!fph) - return; - WARN_ON_ONCE(!futex_private_hash_get(fph)); -} - -void futex_hash_put(struct futex_hash_bucket *hb) -{ - struct futex_private_hash *fph = hb->priv; - - if (!fph) - return; - futex_private_hash_put(fph); -} - static struct futex_hash_bucket * __futex_hash_private(union futex_key *key, struct futex_private_hash *fph) { u32 hash; - if (!futex_key_is_private(key)) - return NULL; - - if (!fph) - fph = rcu_dereference(key->private.mm->futex_phash); - if (!fph || !fph->hash_mask) - return NULL; - hash = jhash2((void *)&key->private.address, sizeof(key->private.address) / 4, key->both.offset); @@ -211,13 +169,12 @@ static void futex_rehash_private(struct futex_private_hash *old, spin_lock(&hb_old->lock); plist_for_each_entry_safe(this, tmp, &hb_old->chain, list) { - plist_del(&this->list, &hb_old->chain); futex_hb_waiters_dec(hb_old); WARN_ON_ONCE(this->lock_ptr != &hb_old->lock); - hb_new = __futex_hash(&this->key, new); + hb_new = __futex_hash(&this->key, new, NULL); futex_hb_waiters_inc(hb_new); /* * The new pointer isn't published yet but an already @@ -271,9 +228,8 @@ static void futex_pivot_hash(struct mm_struct *mm) } } -struct futex_private_hash *futex_private_hash(void) +struct futex_private_hash *futex_private_hash(struct mm_struct *mm) { - struct mm_struct *mm = current->mm; /* * Ideally we don't loop. If there is a replacement in progress * then a new private hash is already prepared and a reference can't be @@ -299,18 +255,17 @@ struct futex_private_hash *futex_private_hash(void) goto again; } -struct futex_hash_bucket *futex_hash(union futex_key *key) +struct futex_bucket_ref futex_hash(union futex_key *key) { - struct futex_private_hash *fph; - struct futex_hash_bucket *hb; - again: scoped_guard(rcu) { - hb = __futex_hash(key, NULL); - fph = hb->priv; + struct futex_private_hash *fph = NULL; + struct futex_hash_bucket *hb; + + hb = __futex_hash(key, NULL, &fph); if (!fph || futex_private_hash_get(fph)) - return hb; + return (struct futex_bucket_ref){ .hb = hb, .fph = fph }; } futex_pivot_hash(key->private.mm); goto again; @@ -318,15 +273,9 @@ struct futex_hash_bucket *futex_hash(union futex_key *key) #else /* !CONFIG_FUTEX_PRIVATE_HASH */ -static struct futex_hash_bucket * -__futex_hash_private(union futex_key *key, struct futex_private_hash *fph) +struct futex_bucket_ref futex_hash(union futex_key *key) { - return NULL; -} - -struct futex_hash_bucket *futex_hash(union futex_key *key) -{ - return __futex_hash(key, NULL); + return (struct futex_bucket_ref){ .hb = __futex_hash(key, NULL, NULL), .fph = NULL }; } #endif /* CONFIG_FUTEX_PRIVATE_HASH */ @@ -412,18 +361,22 @@ static int futex_mpol(struct mm_struct *mm, unsigned long addr) * global hash is returned. */ static struct futex_hash_bucket * -__futex_hash(union futex_key *key, struct futex_private_hash *fph) +__futex_hash(union futex_key *key, struct futex_private_hash *fph, struct futex_private_hash **fph_p) { int node = key->both.node; u32 hash; - if (node == FUTEX_NO_NODE) { - struct futex_hash_bucket *hb; - - hb = __futex_hash_private(key, fph); - if (hb) - return hb; +#ifdef CONFIG_FUTEX_PRIVATE_HASH + if (node == FUTEX_NO_NODE && futex_key_is_private(key)) { + if (!fph) + fph = rcu_dereference(key->private.mm->futex_phash); + if (fph && fph->hash_mask) { + if (fph_p) + *fph_p = fph; + return __futex_hash_private(key, fph); + } } +#endif hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / sizeof(u32), @@ -1336,7 +1289,7 @@ static void exit_pi_state_list(struct task_struct *curr) * on the mutex. */ WARN_ON(curr != current); - guard(private_hash)(); + guard(private_hash)(current->mm); /* * We are a ZOMBIE and nobody can enqueue itself on * pi_state_list anymore, but we have to be careful @@ -1348,7 +1301,8 @@ static void exit_pi_state_list(struct task_struct *curr) pi_state = list_entry(next, struct futex_pi_state, list); key = pi_state->key; if (1) { - CLASS(hb, hb)(&key); + CLASS(hbr, hbr)(&key); + auto hb = hbr.hb; /* * We can race against put_pi_state() removing itself from the @@ -1516,12 +1470,8 @@ void futex_exit_release(struct task_struct *tsk) futex_cleanup_end(tsk, FUTEX_STATE_DEAD); } -static void futex_hash_bucket_init(struct futex_hash_bucket *fhb, - struct futex_private_hash *fph) +static void futex_hash_bucket_init(struct futex_hash_bucket *fhb) { -#ifdef CONFIG_FUTEX_PRIVATE_HASH - fhb->priv = fph; -#endif atomic_set(&fhb->waiters, 0); plist_head_init(&fhb->chain); spin_lock_init(&fhb->lock); @@ -1822,7 +1772,7 @@ static int futex_hash_allocate(unsigned int hash_slots, unsigned int flags) fph->mm = mm; for (i = 0; i < hash_slots; i++) - futex_hash_bucket_init(&fph->queues[i], fph); + futex_hash_bucket_init(&fph->queues[i]); if (custom) { /* @@ -2001,7 +1951,7 @@ static int __init futex_init(void) BUG_ON(!table); for (i = 0; i < hashsize; i++) - futex_hash_bucket_init(&table[i], NULL); + futex_hash_bucket_init(&table[i]); futex_queues[n] = table; } diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h index 9f6bf6f585fc..7aec5e85e039 100644 --- a/kernel/futex/futex.h +++ b/kernel/futex/futex.h @@ -126,6 +126,15 @@ static inline bool should_fail_futex(bool fshared) } #endif +static inline bool futex_key_is_private(union futex_key *key) +{ + /* + * Relies on get_futex_key() to set either bit for shared + * futexes -- see comment with union futex_key. + */ + return !(key->both.offset & (FUT_OFF_INODE | FUT_OFF_MMSHARED)); +} + /* * Hash buckets are shared by all the futex_keys that hash to the same * location. Each key may have multiple futex_q structures, one for each task @@ -135,7 +144,6 @@ struct futex_hash_bucket { atomic_t waiters; spinlock_t lock; struct plist_head chain; - struct futex_private_hash *priv; } ____cacheline_aligned_in_smp; /* @@ -175,7 +183,7 @@ typedef void (futex_wake_fn)(struct wake_q_head *wake_q, struct futex_q *q); * @requeue_pi_key: the requeue_pi target futex key * @bitset: bitset for the optional bitmasked wakeup * @requeue_state: State field for futex_requeue_pi() - * @drop_hb_ref: Waiter should drop the extra hash bucket reference if true + * @drop_fph: Waiter should drop the extra private hash reference when set * @requeue_wait: RCU wait for futex_requeue_pi() (RT only) * * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so @@ -202,7 +210,7 @@ struct futex_q { union futex_key *requeue_pi_key; u32 bitset; atomic_t requeue_state; - bool drop_hb_ref; + struct futex_private_hash *drop_fph; #ifdef CONFIG_PREEMPT_RT struct rcuwait requeue_wait; #endif @@ -222,28 +230,29 @@ extern struct hrtimer_sleeper * futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout, int flags, u64 range_ns); -extern struct futex_hash_bucket *futex_hash(union futex_key *key); -#ifdef CONFIG_FUTEX_PRIVATE_HASH -extern void futex_hash_get(struct futex_hash_bucket *hb); -extern void futex_hash_put(struct futex_hash_bucket *hb); +struct futex_bucket_ref { + struct futex_hash_bucket *hb; + struct futex_private_hash *fph; +}; -extern struct futex_private_hash *futex_private_hash(void); +#ifdef CONFIG_FUTEX_PRIVATE_HASH +extern struct futex_private_hash *futex_private_hash(struct mm_struct *mm); extern void futex_private_hash_put(struct futex_private_hash *fph); #else /* !CONFIG_FUTEX_PRIVATE_HASH */ -static inline void futex_hash_get(struct futex_hash_bucket *hb) { } -static inline void futex_hash_put(struct futex_hash_bucket *hb) { } -static inline struct futex_private_hash *futex_private_hash(void) { return NULL; } +static inline struct futex_private_hash *futex_private_hash(struct mm_struct *mm) { return NULL; } static inline void futex_private_hash_put(struct futex_private_hash *fph) { } #endif -DEFINE_CLASS(hb, struct futex_hash_bucket *, - if (_T) futex_hash_put(_T), +extern struct futex_bucket_ref futex_hash(union futex_key *key); + +DEFINE_CLASS(hbr, struct futex_bucket_ref, + if (_T.fph) futex_private_hash_put(_T.fph), futex_hash(key), union futex_key *key); DEFINE_CLASS(private_hash, struct futex_private_hash *, if (_T) futex_private_hash_put(_T), - futex_private_hash(), void); + futex_private_hash(mm), struct mm_struct *mm); /** * futex_match - Check whether two futex keys are equal diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c index 643199fdbe62..acc8f715c7da 100644 --- a/kernel/futex/pi.c +++ b/kernel/futex/pi.c @@ -945,7 +945,8 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl retry_private: if (1) { - CLASS(hb, hb)(&q.key); + CLASS(hbr, hbr)(&q.key); + auto hb = hbr.hb; futex_q_lock(&q, hb); @@ -1009,7 +1010,7 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl * the thread, performing resize, will block on hb->lock during * the requeue. */ - futex_hash_put(no_free_ptr(hb)); + futex_private_hash_put(no_free_ptr(hbr.fph)); /* * Must be done before we enqueue the waiter, here is unfortunately * under the hb lock, but that *should* work because it does nothing. @@ -1100,11 +1101,9 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl __release(&hb->lock); futex_unqueue_pi(&q); spin_unlock(q.lock_ptr); - if (q.drop_hb_ref) { - CLASS(hb, hb)(&q.key); - /* Additional reference from futex_unlock_pi() */ - futex_hash_put(hb); - } + + /* Additional reference from futex_unlock_pi() */ + futex_private_hash_put(q.drop_fph); goto out; out_unlock_put_key: @@ -1162,7 +1161,8 @@ int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) if (ret) return ret; - CLASS(hb, hb)(&key); + CLASS(hbr, hbr)(&key); + auto hb = hbr.hb; spin_lock(&hb->lock); retry_hb: @@ -1219,8 +1219,9 @@ int futex_unlock_pi(u32 __user *uaddr, unsigned int flags) * Acquire a reference for the leaving waiter to ensure * valid futex_q::lock_ptr. */ - futex_hash_get(hb); - top_waiter->drop_hb_ref = true; + if (futex_key_is_private(&key)) + top_waiter->drop_fph = futex_private_hash(key.private.mm); + __futex_unqueue(top_waiter); raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock); goto retry_hb; diff --git a/kernel/futex/requeue.c b/kernel/futex/requeue.c index 1d99a84dc9ad..7384672916fb 100644 --- a/kernel/futex/requeue.c +++ b/kernel/futex/requeue.c @@ -241,8 +241,8 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key, * Acquire a reference for the waiter to ensure valid * futex_q::lock_ptr. */ - futex_hash_get(hb); - q->drop_hb_ref = true; + if (futex_key_is_private(key)) + q->drop_fph = futex_private_hash(key->private.mm); q->lock_ptr = &hb->lock; task = READ_ONCE(q->task); @@ -459,8 +459,10 @@ int futex_requeue(u32 __user *uaddr1, unsigned int flags1, retry_private: if (1) { - CLASS(hb, hb1)(&key1); - CLASS(hb, hb2)(&key2); + CLASS(hbr, hbr1)(&key1); + CLASS(hbr, hbr2)(&key2); + auto hb1 = hbr1.hb; + auto hb2 = hbr2.hb; futex_hb_waiters_inc(hb2); double_lock_hb(hb1, hb2); @@ -838,7 +840,8 @@ int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, switch (futex_requeue_pi_wakeup_sync(&q)) { case Q_REQUEUE_PI_IGNORE: { - CLASS(hb, hb)(&q.key); + CLASS(hbr, hbr)(&q.key); + auto hb = hbr.hb; /* The waiter is still on uaddr1 */ spin_lock(&hb->lock); ret = handle_early_requeue_pi_wakeup(hb, &q, to); @@ -908,11 +911,8 @@ int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, default: BUG(); } - if (q.drop_hb_ref) { - CLASS(hb, hb)(&q.key); - /* Additional reference from requeue_pi_wake_futex() */ - futex_hash_put(hb); - } + /* Additional reference from requeue_pi_wake_futex() */ + futex_private_hash_put(q.drop_fph); out: if (to) { diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c index ceed9d879059..1f15fff4ada5 100644 --- a/kernel/futex/waitwake.c +++ b/kernel/futex/waitwake.c @@ -169,7 +169,8 @@ int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) if ((flags & FLAGS_STRICT) && !nr_wake) return 0; - CLASS(hb, hb)(&key); + CLASS(hbr, hbr)(&key); + auto hb = hbr.hb; /* Make sure we really have tasks to wakeup */ if (!futex_hb_waiters_pending(hb)) @@ -266,8 +267,10 @@ int futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2, retry_private: if (1) { - CLASS(hb, hb1)(&key1); - CLASS(hb, hb2)(&key2); + CLASS(hbr, hbr1)(&key1); + CLASS(hbr, hbr2)(&key2); + auto hb1 = hbr1.hb; + auto hb2 = hbr2.hb; double_lock_hb(hb1, hb2); op_ret = futex_atomic_op_inuser(op, uaddr2); @@ -409,7 +412,7 @@ int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken) * Make sure to have a reference on the private_hash such that we * don't block on rehash after changing the task state below. */ - guard(private_hash)(); + guard(private_hash)(current->mm); /* * Enqueuing multiple futexes is tricky, because we need to enqueue @@ -446,7 +449,8 @@ int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *woken) u32 val = vs[i].w.val; if (1) { - CLASS(hb, hb)(&q->key); + CLASS(hbr, hbr)(&q->key); + auto hb = hbr.hb; futex_q_lock(q, hb); ret = futex_get_value_locked(&uval, uaddr); @@ -621,7 +625,8 @@ int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags, retry_private: if (1) { - CLASS(hb, hb)(&q->key); + CLASS(hbr, hbr)(&q->key); + auto hb = hbr.hb; futex_q_lock(q, hb);