From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 6C65A1BD9D0; Sun, 10 May 2026 22:45:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778453113; cv=none; b=kFmBV2RGP8hOY+o3yZmUClc63ok2+qimV5qIZH1nmn2+nAMWN9wWJV0TpVPoYPXDqgdb6hwDEQ5ArnbrOeBcQPIs0jYPwGZPB7oiikdeMFU4NmoGc26yegFZs+37Mk4hcQ0s0fMxYZknBk36bXTmur9JfeAnoy+QiQDlNDfBxqI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778453113; c=relaxed/simple; bh=u7oT9dI7oHt2t0S/vOkQmQ9XaiEoHNZB3DMdwiRjWIs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Iy5xvMNeKFw/FljpDwutZpYHzUXhZVwRI2a22ZPBtcQ9vZuDWBpac49tSMW5ze9aWefef/1j3BDSDySKP/aaulIE6fILMttCrwutkC7wTkWCGby/9yyHOBN3SmGCzT/XY2uJ1mV8FoJkwWEONnaexqR0d4ryqrWHqM99SnQ+aeI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bBY0C7x6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bBY0C7x6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDA33C2BCB8; Sun, 10 May 2026 22:45:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778453113; bh=u7oT9dI7oHt2t0S/vOkQmQ9XaiEoHNZB3DMdwiRjWIs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bBY0C7x6ZtLEOtInpyoySZgEZQmOToHB/eFPX4B+rXg1netAGe+rmCdqEFHSYcr5y bElfrMKmCQX4xA7dKIKxQq1c/HcWmx6F3vgjyIdToOEXEUYbPDHNXkj+xMF9DX5csY nFoTRds8+3KxvyqWFvUM5JTzScSdVhWCi3B/gpAGewg98K00tug52za1YEHYYQXX1y mietfROyUxSWqpN/xyLc8OF3g4qFHfBL4epdBtG/XS+P5takp3CV58O2k4s/dUo9vx v1jNjH7B2z8qf7nGYCVhjsPM3iAcviPmBUhRJmGuWhecqNYOli6DOiiheFAv7IWxkR HUKSRD9yzmmNg== From: Tejun Heo To: void@manifault.com, arighi@nvidia.com, changwoo@igalia.com Cc: emil@etsalapatis.com, sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH v2 sched_ext/for-7.2] sched_ext: Add scx_task_iter_relock() and use it in scx_root_enable_workfn() Date: Sun, 10 May 2026 12:45:11 -1000 Message-ID: <20260510224511.2683323-1-tj@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260510222302.2614731-1-tj@kernel.org> References: <20260510222302.2614731-1-tj@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit scx_root_enable_workfn()'s post-init block re-acquires scx_tasks_lock briefly via a scoped_guard() for the tid hash insertion. c941d7391f25 ("sched_ext: Close root-enable vs sched_ext_dead() race with SCX_TASK_INIT_BEGIN") on for-7.1-fixes adds a post-init DEAD recheck that holds the task's rq lock across the state-machine updates in the same region. A naive merge would acquire scx_tasks_lock while the rq lock is held, inverting the iter's outer/inner order (scx_tasks_lock then rq lock). Add scx_task_iter_relock(iter, p), the counterpart to scx_task_iter_unlock(), that re-acquires scx_tasks_lock and, if @p is non-NULL, @p's rq lock. The locks are tracked in @iter so subsequent iteration releases them. Use it in scx_root_enable_workfn()'s post-init block and drop the now-redundant scoped_guard on the hash insertion. The post-init region now runs with both scx_tasks_lock and the task's rq lock held across the init failure check, the state-machine updates and the hash insert. v2: Move scx_task_iter_relock() earlier to ease the for-7.1-fixes merge. Signed-off-by: Tejun Heo --- Applied to sched_ext/for-7.2 to resolve the merge conflict from for-7.1-fixes. kernel/sched/ext.c | 34 ++++++++++++++++++++++++++-------- 1 file changed, 26 insertions(+), 8 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index b685f45b4fd0..fbdc1819d4cb 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -902,6 +902,24 @@ static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter) } } +/** + * scx_task_iter_relock - Re-acquire scx_tasks_lock and, optionally, @p's rq + * @iter: iterator to relock + * @p: task whose rq to lock, or %NULL for scx_tasks_lock only + * + * Counterpart to scx_task_iter_unlock(). Locking @p's rq is optional. Once + * re-acquired, both locks are managed by the iterator from here on. + */ +static void scx_task_iter_relock(struct scx_task_iter *iter, + struct task_struct *p) +{ + __scx_task_iter_maybe_relock(iter); + if (p) { + iter->rq = task_rq_lock(p, &iter->rf); + iter->locked_task = p; + } +} + /** * scx_task_iter_stop - Stop a task iteration and unlock scx_tasks_lock * @iter: iterator to exit @@ -7064,6 +7082,9 @@ static void scx_root_enable_workfn(struct kthread_work *work) scx_task_iter_unlock(&sti); ret = scx_init_task(sch, p, false); + + scx_task_iter_relock(&sti, p); + if (ret) { put_task_struct(p); scx_task_iter_stop(&sti); @@ -7076,15 +7097,12 @@ static void scx_root_enable_workfn(struct kthread_work *work) scx_set_task_state(p, SCX_TASK_READY); /* - * Insert into the tid hash under scx_tasks_lock so we can't - * race sched_ext_dead() and leave a stale entry for an already - * exited task. + * Insert into the tid hash. scx_tasks_lock is held by the iter; + * list_empty() guards against sched_ext_dead() having taken @p + * off the list while init ran unlocked. */ - if (scx_tid_to_task_enabled()) { - guard(raw_spinlock_irq)(&scx_tasks_lock); - if (!list_empty(&p->scx.tasks_node)) - scx_tid_hash_insert(p); - } + if (scx_tid_to_task_enabled() && !list_empty(&p->scx.tasks_node)) + scx_tid_hash_insert(p); put_task_struct(p); } -- 2.54.0