From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 BAC8624E4AF for ; Mon, 16 Mar 2026 08:06:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773648375; cv=none; b=gEm3GCFZxn0fqbL19E70ER6T5iYHgAZM7PeLuW7qt6Cs+/W+dzgGJMISRe1PhjzRNeOyCbl2jP/1RS8iJg3bYOAtCv3nKwtKVyEq3DxS5gCgqGGNUineXVusTorejX/17/+G4Rh4fK5zMW1jsMz5ULer9pT6PdJCdOYlulI6L0Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773648375; c=relaxed/simple; bh=GPDIjnFjrFITQjFRHxEVmc+rlL/Jh+3l4rzt4hE5ZWI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uadLIlrCf+6tWn5G3w14YYinqkMvuI2f6FNvwe4wnzER0jehsoa3X8oHDNt5n/0PZEiiiEy2V306wn8t02Xq8eu0f8TvfjXdSu3c+edq46BW2HtBgNt27oSke6ZAKX/BciqMBTtVHc5QrS9hRt90Lp0YZK/pGHmU0V3Le3f3KoE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=297OAddl; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=yqB75Mvh; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="297OAddl"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="yqB75Mvh" Date: Mon, 16 Mar 2026 09:06:11 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1773648373; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2T5XEiat4AcyzU2cNJEUVlnoFi/dWcIq2LJ23mESUlQ=; b=297OAddlSqXv+JWNuPL/agpbOXlSRSEdJ4X0A46FZ3Vfh5J/3+G+HmI7LrE+O08+8XCpcH +xXvNLLdXivv6ZktD/KcdTajNnh8pROsU0OaixM9BIEDYmHL4S9cxXqYJ8CiBV4zfQoaai IAjAYDaWtWIRrOOxYJvNtMKhA+l+BsAR3IJjupN9G566vrHmOZFzriPj4jEg8QNK6fYVY0 QCzvlZvaLWXOVGZ4wVlEVpixRhQ3yND5sMB9S0qQXBxyFsWGxO7DiOZKPEJpesv4xB43vL fjY6RDqSprBQuPv1nAkiUcVpI9R0pEju7ba7qh70oitikIsNho0QKQYWsb/mhg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1773648373; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2T5XEiat4AcyzU2cNJEUVlnoFi/dWcIq2LJ23mESUlQ=; b=yqB75MvhOX5CY6ecyoO4t/jgjahEVW9oU7TCaA2rmG0yXrrNvZ43z8SbZO3kbFfxsBKqKx BRdNh/ntIqYBfbBw== From: Sebastian Andrzej Siewior To: Tejun Heo Cc: Michal =?utf-8?Q?Koutn=C3=BD?= , cgroups@vger.kernel.org, linux-rt-devel@lists.linux.dev, Ben Segall , Clark Williams , Dietmar Eggemann , Ingo Molnar , Johannes Weiner , Juri Lelli , Mel Gorman , Peter Zijlstra , Steven Rostedt , Valentin Schneider , Vincent Guittot Subject: Re: [PATCH] cgroup: Move cgroup_task_dead() to task_struct clean up Message-ID: <20260316080611.5G06G5O8@linutronix.de> References: <20260311120829.rEHY-xh9@linutronix.de> <20260314091752.B7CXvQxn@linutronix.de> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 2026-03-15 10:15:41 [-1000], Tejun Heo wrote: > Hello, Hi, > Yeah, I think it's too late. That's where we tell the cgroup is becoming > empty among other things. cgroup_task_free() waits for all task refcnts to > drop which can take any amount of time. You can also imagine situations > where e.g. userspace pins a specific task through pidfd unitl the cgroup it > belongs becomes empty, which would have worked before but now would > deadlock. I see. What about moving it to delayed_put_task_struct() such as the change on top below? It also RCU and only acquired by bpf_task_acquire(). Is this also a concern or would that work? --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -138,6 +138,7 @@ extern void cgroup_cancel_fork(struct task_struct *p, extern void cgroup_post_fork(struct task_struct *p, struct kernel_clone_args *kargs); void cgroup_task_exit(struct task_struct *p); +void cgroup_task_dead(struct task_struct *p); void cgroup_task_release(struct task_struct *p); void cgroup_task_free(struct task_struct *p); @@ -681,6 +682,7 @@ static inline void cgroup_cancel_fork(struct task_struct *p, static inline void cgroup_post_fork(struct task_struct *p, struct kernel_clone_args *kargs) {} static inline void cgroup_task_exit(struct task_struct *p) {} +static inline void cgroup_task_dead(struct task_struct *p) {} static inline void cgroup_task_release(struct task_struct *p) {} static inline void cgroup_task_free(struct task_struct *p) {} diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 684b773cd5cb4..28cdb8d3210e7 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -6991,7 +6991,7 @@ void cgroup_task_exit(struct task_struct *tsk) } while_each_subsys_mask(); } -static void cgroup_task_dead(struct task_struct *tsk) +void cgroup_task_dead(struct task_struct *tsk) { struct css_set *cset; unsigned long flags; @@ -7031,7 +7031,6 @@ void cgroup_task_free(struct task_struct *task) { struct css_set *cset = task_css_set(task); - cgroup_task_dead(task); if (!list_empty(&task->cg_list)) { spin_lock_irq(&css_set_lock); css_set_skip_task_iters(task_css_set(task), task); diff --git a/kernel/exit.c b/kernel/exit.c index ede3117fa7d41..7a94425122238 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -228,6 +228,7 @@ static void delayed_put_task_struct(struct rcu_head *rhp) rethook_flush_task(tsk); perf_event_delayed_put(tsk); trace_sched_process_free(tsk); + cgroup_task_dead(tsk); put_task_struct(tsk); } > Thanks. Sebastian