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Sun, 9 Feb 2025 22:30:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1739140216; bh=Wqntl1ggAaL74aa0p3y2a++/5r9dcdOK0C0/zF8B/OM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KAPDlktuV4x4lOY7dt1MX379eFc7iOHZYEvyz50M+V1vMYLZ7fvi/DNn8BHL0uWC0 cXq25hvD0Trn40F1pWIwz9IczyCePognvXVQCGaIAKDvM2xUvzI6+hvU03b5Cy6676 LrZm7F5c4pvdz6EE7y7SE2gv1dj+bDk7jWASzAw/FMf9AVm6+e4zikrFJvFmLs4lOd 5iO3Oxaf7du0MevTy+0WWhJdedrBIABnQJ9GZ2QAeADelMF09h3j9edOOY4Ltj8gEI 9LAaHzsaa8DCVFuBbzU19CGwd0mRHpbQgpwddFBVCMCemNmiHRz8OEsri+qzxovymK LVdtWCPkeLQxA== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Peter Zijlstra , Ingo Molnar , Valentin Schneider , Marcelo Tosatti , Vlastimil Babka , Andrew Morton , Michal Hocko , Thomas Gleixner , Oleg Nesterov , linux-mm@kvack.org Subject: [PATCH 1/6 v2] task_work: Provide means to check if a work is queued Date: Sun, 9 Feb 2025 23:29:59 +0100 Message-ID: <20250209223005.11519-2-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20250209223005.11519-1-frederic@kernel.org> References: <20250209223005.11519-1-frederic@kernel.org> MIME-Version: 1.0 X-Rspam-User: X-Stat-Signature: y7etra196i9poxwsptf448koj16k1rur X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 353E8140005 X-HE-Tag: 1739140217-433472 X-HE-Meta: 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 mnahSVfT OWhZxQ0WJ9gHLXoAHnvw6FFJJkofYZUId++hevg6e3LcCpHXH8dyaq9vZEtV+giEZPuVhzTiEzcHUIjA9FAmYzPa2bwhynlVvTEUEF+qoXdvxgQEYZNtC0Ozy+FCzZgUfa/HIAb5vyoTBzv5COn4/Fs7yKTGV/dUxTSeUIWtyervxodr4HHmU5f8pBaJModHIm/IrTutHJLkHcdNhQaXskkZ5rlbgORIUH/awZ4Zlyt+5KbJnsblsiIkbZxUj/bIZrC9jz3lZNQy4kTAlgUkx2lrSThU8L7PhSP8pa/v1VnHFay/tKV9fgymlRQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Some task work users implement their own ways to know if a callback is already queued on the current task while fiddling with the callback head internals. Provide instead a consolidated API to serve this very purpose. Signed-off-by: Frederic Weisbecker Reviewed-by: Oleg Nesterov --- include/linux/task_work.h | 12 ++++++++++++ kernel/task_work.c | 11 +++++++++-- 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/include/linux/task_work.h b/include/linux/task_work.h index 0646804860ff..31caf12c1313 100644 --- a/include/linux/task_work.h +++ b/include/linux/task_work.h @@ -5,12 +5,15 @@ #include #include +#define TASK_WORK_DEQUEUED ((void *) -1UL) + typedef void (*task_work_func_t)(struct callback_head *); static inline void init_task_work(struct callback_head *twork, task_work_func_t func) { twork->func = func; + twork->next = TASK_WORK_DEQUEUED; } enum task_work_notify_mode { @@ -26,6 +29,15 @@ static inline bool task_work_pending(struct task_struct *task) return READ_ONCE(task->task_works); } +/* + * Check if a work is queued. Beware: this is inherently racy if the work can + * be queued elsewhere than the current task. + */ +static inline bool task_work_queued(struct callback_head *twork) +{ + return twork->next != TASK_WORK_DEQUEUED; +} + int task_work_add(struct task_struct *task, struct callback_head *twork, enum task_work_notify_mode mode); diff --git a/kernel/task_work.c b/kernel/task_work.c index d1efec571a4a..0d7b04095753 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -56,6 +56,8 @@ int task_work_add(struct task_struct *task, struct callback_head *work, { struct callback_head *head; + work->next = TASK_WORK_DEQUEUED; + if (notify == TWA_NMI_CURRENT) { if (WARN_ON_ONCE(task != current)) return -EINVAL; @@ -67,8 +69,10 @@ int task_work_add(struct task_struct *task, struct callback_head *work, head = READ_ONCE(task->task_works); do { - if (unlikely(head == &work_exited)) + if (unlikely(head == &work_exited)) { + work->next = TASK_WORK_DEQUEUED; return -ESRCH; + } work->next = head; } while (!try_cmpxchg(&task->task_works, &head, work)); @@ -129,8 +133,10 @@ task_work_cancel_match(struct task_struct *task, if (!match(work, data)) { pprev = &work->next; work = READ_ONCE(*pprev); - } else if (try_cmpxchg(pprev, &work, work->next)) + } else if (try_cmpxchg(pprev, &work, work->next)) { + work->next = TASK_WORK_DEQUEUED; break; + } } raw_spin_unlock_irqrestore(&task->pi_lock, flags); @@ -224,6 +230,7 @@ void task_work_run(void) do { next = work->next; + work->next = TASK_WORK_DEQUEUED; work->func(work); work = next; cond_resched();