From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 2FD4E31F99E for ; Tue, 5 May 2026 14:22:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777990926; cv=none; b=eCgJSHDPRaUOHNwlBZkElabbV2DV4AmgYiecsMbDvkrTSIXDKWw8ZDx6wStIaCywMWdNjbNK4bIEllP7SxMeIv/oqxPApppkLQVHYx7b6V566GtJSidn8XgIQyoMbKu63x951BGKjJmHZ2oYXYGdoWWNLpW9/Jofpfdyn9TTlZg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777990926; c=relaxed/simple; bh=WaCn6cSE6c3EIldRIlS5W/LPD3rlBHG4K2wtGwGG4qA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qxB9ixKKCUgWHLgBYZYU44OXETKngu/wWboJSH0FPRX22BdaQkj5uu2NFFVKM451PrywM8dNoGxiPMXTS1Z1BAGZmkyn5b16sN0b1Utw/L+GgxPXQKORlQbHVgH4kEI0i3CN+9bLSIoa7emH3sGblG4s3ALFaDUCyej8mCGFcjE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=s3InSHRW; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="s3InSHRW" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=36mo/RbE1Rm6ksRenGPEp1nCzYhMc4Y6VfyMJOT5g7o=; b=s3InSHRWrdXLgLQ/nMu6AYrTJ1 KUzTIz+cUiIZMc3Zm8l3uu+V5FdxQewP48qtLOM9fx22z6yZ4NQwVZgES4Lo9wf5gjSerM656hiHT ZgHM6//SnKuJPoQ0OW+3wYnxz9RpMrN7yU/PiRc2uJgkTLvkrpqQwRvlQoq/NNX8f2Oh2BNpfd14g CuFODemQJIVsUJQ7KKhMwydhsNxN0tfyU5E1BoQ/lZ1D9tduHaMtgp37k43swVE3u67VKSpdVUH2O tLDEk+wCFX8NHl0sMYI+MIwjurf3MaPoysZligSQ+/nvQblZLjGBTmjqipWmDmoq3erF9Qhkm4T/J DXXSfRUA==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99.1 #2 (Red Hat Linux)) id 1wKGfF-00000006YiC-43b4; Tue, 05 May 2026 14:22:22 +0000 Date: Tue, 5 May 2026 15:22:21 +0100 From: Al Viro To: NeilBrown Cc: Linus Torvalds , linux-fsdevel@vger.kernel.org, Christian Brauner , Jan Kara Subject: Re: [RFC PATCH 12/25] reducing rcu_read_lock() scopes in dput and friends, step 1 Message-ID: <20260505142221.GD3518998@ZenIV> References: <20260505055412.1261144-1-viro@zeniv.linux.org.uk> <20260505055412.1261144-13-viro@zeniv.linux.org.uk> <177797133377.1474915.1770170197135589795@noble.neil.brown.name> Precedence: bulk X-Mailing-List: linux-fsdevel@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: <177797133377.1474915.1770170197135589795@noble.neil.brown.name> Sender: Al Viro On Tue, May 05, 2026 at 06:55:33PM +1000, NeilBrown wrote: > On Tue, 05 May 2026, Al Viro wrote: > > rcu_read_lock() scopes in dentry eviction machinery are too wide; > > worse, quite a few of the function involved are not neutral wrt > > that, making them harder to reason about. > > > > rcu_read_lock() scope is not the only thing establishing an > > RCU read-side critical area - spin_lock scope does the same and > > they can be mixed - the sequence > > Does it? I can't find any document or code which supports that clain. > Could you provide a pointer? Documentation/RCU/whatisRCU.rst in the section on rcu_read_unlock(). See the subthread back in April: https://lore.kernel.org/all/CAHk-=wjRgHLvSnEY3P45hSQ0ycKxdz-xqnccAMPuGRrwsvWdig@mail.gmail.com/ including this, for example: https://lore.kernel.org/all/4e59837d-567b-4678-8a15-e933def32fcb@paulmck-laptop/ Basically, "if ain't true, RCU implementation has a bug that needs fixing"