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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a02738654csm4291269a91.3.2026.09.19.15.17.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 15:17:30 -0700 (PDT) From: Hui Peng To: tglx@kernel.org, mingo@redhat.com, peterz@infradead.org, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@igalia.com Cc: linux-kernel@vger.kernel.org Subject: [PATCH] futex: fix hb lock mismatch in futex_wait_requeue_pi() and CLONE_VFORK hash init Date: Sat, 19 Sep 2026 22:17:30 +0000 Message-ID: <20260919221730.3707261-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Fix two issues in futex and fork initialization: 1. In futex_wait_requeue_pi(), if futex_wait_queue() returns with q.lock_ptr updated tohb2's lock after a requeue timeout or signal race, unlocking the original hb1 lock instead of q.lock_ptr leaves hb2 locked and unlocks an unheld spinlock. Always unlock via q.lock_ptr. 2. In copy_mm() (kernel/fork.c), initialize mm->futex_phash properly when cloning so private futex hash state is consistent across CLONE_VFORK. Fixes: e5c6828493b5 ("futex: Split out requeue") Assisted-by: LLM Signed-off-by: Hui Peng --- diff --git a/kernel/fork.c b/kernel/fork.c index a5934a317634..8f320f51cae8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1996,9 +1996,9 @@ static bool need_futex_hash_allocate_default(u64 clone_flags) { /* * Allocate a default futex hash for any sibling that will - * share the parent's mm, except vfork. + * share the parent's mm. */ - return (clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM; + return (clone_flags & CLONE_VM) != 0; } /* diff --git a/kernel/futex/requeue.c b/kernel/futex/requeue.c index b3f4a4bccb12..72b954d625c4 100644 --- a/kernel/futex/requeue.c +++ b/kernel/futex/requeue.c @@ -842,12 +842,13 @@ int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, switch (futex_requeue_pi_wakeup_sync(&q)) { case Q_REQUEUE_PI_IGNORE: { - CLASS(hbr, hbr)(&q.key); - auto hb = hbr.hb; + struct futex_hash_bucket *hb; + /* The waiter is still on uaddr1 */ - spin_lock(&hb->lock); + futex_q_lockptr_lock(&q); + hb = container_of(q.lock_ptr, struct futex_hash_bucket, lock); ret = handle_early_requeue_pi_wakeup(hb, &q, to); - spin_unlock(&hb->lock); + spin_unlock(q.lock_ptr); } break;