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AJvYcCUADs86zzm2QXhucK1DNVNVgJbR6kZPBe46t25QJPVJnR7fYteU+jcqzHMMvod2r3PRs6cnD+UKlxkufzdo3R3Q@lists.infradead.org X-Gm-Message-State: AOJu0Yy6TRk3K8d6iwwRdHXrROVNDazccLzdy48boXx91UDugTojGQBO p1aK2pQaDrdlF4bbWnj7Ii1Lk/IwxgyAjmEiUptUtQUeBENVKOWA0TCtVjYLCXDIhCoi2Am7jOv quw== X-Google-Smtp-Source: AGHT+IFdQSCduwNTHLV/nec9/i/BvW+thtXD97niBCIJ/k+4mEqw+xFFVLw5YdqLnoDpAq+BRV3lhigqiIM= X-Received: from pjk16.prod.google.com ([2002:a17:90b:5590:b0:2ea:5084:5297]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:574b:b0:2ee:9b09:7d3d with SMTP id 98e67ed59e1d1-305320af3e0mr18907665a91.19.1743540418245; Tue, 01 Apr 2025 13:46:58 -0700 (PDT) Date: Tue, 1 Apr 2025 13:44:18 -0700 In-Reply-To: <20250401204425.904001-1-seanjc@google.com> Mime-Version: 1.0 References: <20250401204425.904001-1-seanjc@google.com> X-Mailer: git-send-email 2.49.0.504.g3bcea36a83-goog Message-ID: <20250401204425.904001-7-seanjc@google.com> Subject: [PATCH 06/12] sched/wait: Add a waitqueue helper for fully exclusive priority waiters From: Sean Christopherson To: Paolo Bonzini , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Marc Zyngier , Oliver Upton , Sean Christopherson , Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-riscv@lists.infradead.org, David Matlack , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250401_134659_604429_D8932C86 X-CRM114-Status: GOOD ( 15.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Sean Christopherson Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Add a waitqueue helper to add a priority waiter that requires exclusive wakeups, i.e. that requires that it be the _only_ priority waiter. The API will be used by KVM to ensure that at most one of KVM's irqfds is bound to a single eventfd (across the entire kernel). Open code the helper instead of using __add_wait_queue() so that the common path doesn't need to "handle" impossible failures. Note, the priority_exclusive() name is obviously confusing as the plain priority() API also sets WQ_FLAG_EXCLUSIVE. This will be remedied once KVM switches to add_wait_queue_priority_exclusive(), as the only other user of add_wait_queue_priority(), Xen's privcmd, doesn't actually operate in exclusive mode (more than likely, the detail was overlooked when privcmd copy-pasted (sorry, "was inspired by") KVM's implementation). Signed-off-by: Sean Christopherson --- include/linux/wait.h | 2 ++ kernel/sched/wait.c | 20 ++++++++++++++++++++ 2 files changed, 22 insertions(+) diff --git a/include/linux/wait.h b/include/linux/wait.h index 6d90ad974408..5fe082c9e52b 100644 --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -164,6 +164,8 @@ static inline bool wq_has_sleeper(struct wait_queue_head *wq_head) extern void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry); extern void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry); extern void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry); +extern int add_wait_queue_priority_exclusive(struct wait_queue_head *wq_head, + struct wait_queue_entry *wq_entry); extern void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry); static inline void __add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index 51e38f5f4701..80d90d1dc24d 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -47,6 +47,26 @@ void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_ } EXPORT_SYMBOL_GPL(add_wait_queue_priority); +int add_wait_queue_priority_exclusive(struct wait_queue_head *wq_head, + struct wait_queue_entry *wq_entry) +{ + struct list_head *head = &wq_head->head; + unsigned long flags; + int r = 0; + + wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY; + spin_lock_irqsave(&wq_head->lock, flags); + if (!list_empty(head) && + (list_first_entry(head, typeof(*wq_entry), entry)->flags & WQ_FLAG_PRIORITY)) + r = -EBUSY; + else + list_add(&wq_entry->entry, head); + spin_unlock_irqrestore(&wq_head->lock, flags); + + return r; +} +EXPORT_SYMBOL(add_wait_queue_priority_exclusive); + void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry) { unsigned long flags;