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 2570930B509; Fri, 10 Apr 2026 19:29:05 +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=1775849346; cv=none; b=Cckc02gAbjapf6dbRqCyiCRpykGGfkfr6vOkSFMRMAb5y/7iyF0f5gfmFSVz9hB64zan8M1PM61CVaRnH/GTgdpEzqAD2NTUryohuT+Xe5ULVwGjy9S/MGaMaH1HuCymm7D6Y4Ciaj/1L7nTy8M5sVvBlW3/a/vpFcZKgsVPtRs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775849346; c=relaxed/simple; bh=zy0hAvV+NOwFb5nTFTEz3iYeb2USleR88YYuiS6EvR8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OKl+ClClVDSFnmtb5kpZoRGK+aCUKAShXYKyRBaawR7uFsXt0ZP9VNOOI+ev8CAUoXcAwaE6+jdhyvDXlKkQ7kJXG7cxWp56aSrzdF+ZjoX9YKfu4aUUWYJzh++WJv40E8E1i3f7+iMdfUgGwIsV7SamVPQiHOt/NwH1oRMvPQg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oaIxhMfg; 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="oaIxhMfg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A04B9C19421; Fri, 10 Apr 2026 19:29:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775849345; bh=zy0hAvV+NOwFb5nTFTEz3iYeb2USleR88YYuiS6EvR8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=oaIxhMfg37pjioBpynzVtdgjP1hfBu+X9N+ucjEQuSjRNCze9Kd2Y07X+SGYiWxdD rt0OinSl7bU5elKCd8v88B3zUlBCi5KbqtpYWXoazC+fV2pYnQXM6NAAUYcQX5wgUZ k43fG1P50K7iVkitpYcivDdGuNiliJEG7h6xToBsW8/F8ErLAjvKp4uhW+5ICxqDL3 RjYUn7XuKgC3Xp7wlrvVpYpZHAo67lloSAqioc2JnUFK8v0W6XF3e+iXxUKIp8s0uX UmSjNxZZEnOS7DkJhP7pTBiun1tydlNaVV3e50sD/KxGf0xdD/dfBSP+33xJu8BoBv 2H7nxuryitg0Q== Date: Fri, 10 Apr 2026 09:29:04 -1000 From: Tejun Heo To: "Paul E. McKenney" Cc: Boqun Feng , Vasily Gorbik , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Uladzislau Rezki , rcu@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, Lai Jiangshan Subject: Re: BUG: workqueue lockup - SRCU schedules work on not-online CPUs during size transition Message-ID: References: <25415176-d977-41c1-83d1-3f060292f636@paulmck-laptop> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <25415176-d977-41c1-83d1-3f060292f636@paulmck-laptop> Hello, Paul. On Fri, Apr 10, 2026 at 12:17:21PM -0700, Paul E. McKenney wrote: > > The easiest way to do this is just creating the initial workers for all > > possible pools. Please see below. However, the downside is that it's going > > to create all workers for all possible cpus. This isn't a problem for > > anybody else but these IBM mainframes often come up with a lot of possible > > but not-yet-or-ever-online CPUs for capacity management, so the cost may not > > be negligible on some configurations. > > > > IBM folks, is that okay? > > I have also seen x86 systems whose firmware claimed very large numbers > of CPUs. :-( Yeah, I remember seeing those but at least the ones I remember are from long times ago. Hopefully, no bios is getting things that wrong anymore. > > Also, why do you need to queue work items on an offline CPU? Do they > > actually have to be per-cpu? Can you get away with using an unbound > > workqueue? > > It is good for them to run on the specified CPU in the common case for > cache-locality reasons, but if they were occasionally redirected to some > other CPU, that would be just fine. I see. > I am also keeping the patch that avoids queueing work to CPUs that are not > yet fully online. Further adjustments will be needed if someone invokes > call_srcu(), synchronize_srcu(), or synchronize_srcu_expedited() from an > CPU that is not yet fully online. Past experience of course suggests that > this will be happen, and that there will be a good reason for it. ;-) I'm gonna hold for now. From workqueue side, it's a really easy change, so please let me know if this comes up again. Thanks. -- tejun