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[141.239.158.86]) by smtp.gmail.com with ESMTPSA id o23-20020a056a001b5700b006e025ce0beesm232976pfv.168.2024.02.16.10.06.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Feb 2024 10:06:27 -0800 (PST) Sender: Tejun Heo From: Tejun Heo To: jiangshanlai@gmail.com Cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, allen.lkml@gmail.com, kernel-team@meta.com, Tejun Heo Subject: [PATCH 08/17] workqueue: Factor out work_grab_pending() from __cancel_work_sync() Date: Fri, 16 Feb 2024 08:04:49 -1000 Message-ID: <20240216180559.208276-9-tj@kernel.org> X-Mailer: git-send-email 2.43.2 In-Reply-To: <20240216180559.208276-1-tj@kernel.org> References: <20240216180559.208276-1-tj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1791079899324713922 X-GMAIL-MSGID: 1791079899324713922 The planned disable/enable support will need the same logic. Let's factor it out. No functional changes. Signed-off-by: Tejun Heo --- kernel/workqueue.c | 130 +++++++++++++++++++++++++++------------------ 1 file changed, 78 insertions(+), 52 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 7c6915e23c5c..38e589b6871c 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -484,6 +484,12 @@ static struct workqueue_attrs *unbound_std_wq_attrs[NR_STD_WORKER_POOLS]; /* I: attributes used when instantiating ordered pools on demand */ static struct workqueue_attrs *ordered_wq_attrs[NR_STD_WORKER_POOLS]; +/* + * Used to synchronize multiple cancel_sync attempts on the same work item. See + * work_grab_pending() and __cancel_work_sync(). + */ +static DECLARE_WAIT_QUEUE_HEAD(wq_cancel_waitq); + /* * I: kthread_worker to release pwq's. pwq release needs to be bounced to a * process context while holding a pool lock. Bounce to a dedicated kthread @@ -2147,6 +2153,73 @@ static int try_to_grab_pending(struct work_struct *work, u32 cflags, return -EAGAIN; } +struct cwt_wait { + wait_queue_entry_t wait; + struct work_struct *work; +}; + +static int cwt_wakefn(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) +{ + struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait); + + if (cwait->work != key) + return 0; + return autoremove_wake_function(wait, mode, sync, key); +} + +/** + * work_grab_pending - steal work item from worklist and disable irq + * @work: work item to steal + * @cflags: %WORK_CANCEL_ flags + * + * Grab PENDING bit of @work. @work can be in any stable state - idle, on timer + * or on worklist. + * + * Must be called in process context. IRQ is disabled on return. The caller is + * responsible for re-enabling it using local_irq_enable(). + * + * Returns %true if @work was pending. %false if idle. + */ +static bool work_grab_pending(struct work_struct *work, u32 cflags, + unsigned long *irq_flags) +{ + struct cwt_wait cwait; + int ret; + + might_sleep(); +repeat: + ret = try_to_grab_pending(work, cflags, irq_flags); + if (likely(ret >= 0)) + return ret; + if (ret != -ENOENT) + goto repeat; + + /* + * Someone is already canceling. Wait for it to finish. flush_work() + * doesn't work for PREEMPT_NONE because we may get woken up between + * @work's completion and the other canceling task resuming and clearing + * CANCELING - flush_work() will return false immediately as @work is no + * longer busy, try_to_grab_pending() will return -ENOENT as @work is + * still being canceled and the other canceling task won't be able to + * clear CANCELING as we're hogging the CPU. + * + * Let's wait for completion using a waitqueue. As this may lead to the + * thundering herd problem, use a custom wake function which matches + * @work along with exclusive wait and wakeup. + */ + init_wait(&cwait.wait); + cwait.wait.func = cwt_wakefn; + cwait.work = work; + + prepare_to_wait_exclusive(&wq_cancel_waitq, &cwait.wait, + TASK_UNINTERRUPTIBLE); + if (work_is_canceling(work)) + schedule(); + finish_wait(&wq_cancel_waitq, &cwait.wait); + + goto repeat; +} + /** * insert_work - insert a work into a pool * @pwq: pwq @work belongs to @@ -4125,60 +4198,13 @@ static bool __cancel_work(struct work_struct *work, u32 cflags) return ret; } -struct cwt_wait { - wait_queue_entry_t wait; - struct work_struct *work; -}; - -static int cwt_wakefn(wait_queue_entry_t *wait, unsigned mode, int sync, void *key) -{ - struct cwt_wait *cwait = container_of(wait, struct cwt_wait, wait); - - if (cwait->work != key) - return 0; - return autoremove_wake_function(wait, mode, sync, key); -} - static bool __cancel_work_sync(struct work_struct *work, u32 cflags) { - static DECLARE_WAIT_QUEUE_HEAD(cancel_waitq); unsigned long irq_flags; - int ret; - - do { - ret = try_to_grab_pending(work, cflags, &irq_flags); - /* - * If someone else is already canceling, wait for it to - * finish. flush_work() doesn't work for PREEMPT_NONE - * because we may get scheduled between @work's completion - * and the other canceling task resuming and clearing - * CANCELING - flush_work() will return false immediately - * as @work is no longer busy, try_to_grab_pending() will - * return -ENOENT as @work is still being canceled and the - * other canceling task won't be able to clear CANCELING as - * we're hogging the CPU. - * - * Let's wait for completion using a waitqueue. As this - * may lead to the thundering herd problem, use a custom - * wake function which matches @work along with exclusive - * wait and wakeup. - */ - if (unlikely(ret == -ENOENT)) { - struct cwt_wait cwait; - - init_wait(&cwait.wait); - cwait.wait.func = cwt_wakefn; - cwait.work = work; - - prepare_to_wait_exclusive(&cancel_waitq, &cwait.wait, - TASK_UNINTERRUPTIBLE); - if (work_is_canceling(work)) - schedule(); - finish_wait(&cancel_waitq, &cwait.wait); - } - } while (unlikely(ret < 0)); + bool ret; - /* tell other tasks trying to grab @work to back off */ + /* claim @work and tell other tasks trying to grab @work to back off */ + ret = work_grab_pending(work, cflags, &irq_flags); mark_work_canceling(work); local_irq_restore(irq_flags); @@ -4197,8 +4223,8 @@ static bool __cancel_work_sync(struct work_struct *work, u32 cflags) * visible there. */ smp_mb(); - if (waitqueue_active(&cancel_waitq)) - __wake_up(&cancel_waitq, TASK_NORMAL, 1, work); + if (waitqueue_active(&wq_cancel_waitq)) + __wake_up(&wq_cancel_waitq, TASK_NORMAL, 1, work); return ret; }