From patchwork Tue Nov 12 14:22:37 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederic Weisbecker X-Patchwork-Id: 13872300 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 972532003DB; Tue, 12 Nov 2024 14:23:30 +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=1731421410; cv=none; b=blHpjR1FJreRGQws3gN3ZVnZP4+g4PG1RrCXJI8S09f1JwA+K6mvtk5FlU0rIFcOemcmjz/f6TARYBUiJ4JbgH3ADecowbHUJC2HB4jA00XmugjB7gfLWo//66RPF+z7h4t91qYqMPCTKOXvoFFVz7o94CjF5aIfbzShema1nWs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731421410; c=relaxed/simple; bh=1Mtlm//q48SrsPqs3+PH5LEw1zSw/x3ZR0//41DWXT0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=flY/InRaWfZtuzxFeMTySS8iJl+mRx7iWXTeZVudaqbpwCg975/XgvPTYU7eLIV5yavSjO5/ZCMP/566OzVW5XnIttIIfnecNA631/icB7rmNoQOnwMsWwcB/b7VXRqB4fbR2pD0M+lZ7ACyX/k+k0Io3U+ss9aLRzd0Ea9pFNM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bX6I+zoH; 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="bX6I+zoH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12BFCC4CECD; Tue, 12 Nov 2024 14:23:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731421410; bh=1Mtlm//q48SrsPqs3+PH5LEw1zSw/x3ZR0//41DWXT0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bX6I+zoHIDtpnApj8lTc4/kUq9/Avb5U6PIJXGr6R7ZH+w5tkNcKKlu21bICUDGN/ vayr3D5njBiqePvwXiwHyfN3kXc06v69j6prrZAqfNIOoSrm+C+z3Q4pL4M9q7C9uS wuZcO0UGrrDCK82FPd8TKMDwRf9wA/+UEHiQzK67WXEbvJsJe0NzgqK9g5y85trGjw 1q7fRsyVwt8VkR8OxvGOhleSa7Ia/nqon3h/KDe5lg2kCq7+DLI23O2etxWOwsasvC OoogZcMGZcCTjUSo3xgRwG4+kM9yXk8NPYiZZoznEPGulBno+uw9HmRgV70VCAv/Ql rD/v3aloGzdYQ== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Andrew Morton , Kees Cook , Peter Zijlstra , Thomas Gleixner , Michal Hocko , Vlastimil Babka , linux-mm@kvack.org, "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Zqiang , rcu@vger.kernel.org, Uladzislau Rezki Subject: [PATCH 13/21] kthread: Make sure kthread hasn't started while binding it Date: Tue, 12 Nov 2024 15:22:37 +0100 Message-ID: <20241112142248.20503-14-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20241112142248.20503-1-frederic@kernel.org> References: <20241112142248.20503-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Make sure the kthread is sleeping in the schedule_preempt_disabled() call before calling its handler when kthread_bind[_mask]() is called on it. This provides a sanity check verifying that the task is not randomly blocked later at some point within its function handler, in which case it could be just concurrently awaken, leaving the call to do_set_cpus_allowed() without any effect until the next voluntary sleep. Rely on the wake-up ordering to ensure that the newly introduced "started" field returns the expected value: TASK A TASK B ------ ------ READ kthread->started wake_up_process(B) rq_lock() ... rq_unlock() // RELEASE schedule() rq_lock() // ACQUIRE // schedule task B rq_unlock() WRITE kthread->started Similarly, writing kthread->started before subsequent voluntary sleeps will be visible after calling wait_task_inactive() in __kthread_bind_mask(), reporting potential misuse of the API. Upcoming patches will make further use of this facility. Acked-by: Vlastimil Babka Signed-off-by: Frederic Weisbecker --- kernel/kthread.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/kthread.c b/kernel/kthread.c index 9bb36897b6c6..b9bdb21a0101 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -53,6 +53,7 @@ struct kthread_create_info struct kthread { unsigned long flags; unsigned int cpu; + int started; int result; int (*threadfn)(void *); void *data; @@ -382,6 +383,8 @@ static int kthread(void *_create) schedule_preempt_disabled(); preempt_enable(); + self->started = 1; + ret = -EINTR; if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) { cgroup_kthread_ready(); @@ -540,7 +543,9 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask) { + struct kthread *kthread = to_kthread(p); __kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE); + WARN_ON_ONCE(kthread->started); } /** @@ -554,7 +559,9 @@ void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask) */ void kthread_bind(struct task_struct *p, unsigned int cpu) { + struct kthread *kthread = to_kthread(p); __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE); + WARN_ON_ONCE(kthread->started); } EXPORT_SYMBOL(kthread_bind);