From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 787D8C4452F for ; Tue, 21 Jul 2026 13:10:09 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 35CFB6B008A; Tue, 21 Jul 2026 09:10:08 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 30DB86B008C; Tue, 21 Jul 2026 09:10:08 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1D54E6B0092; Tue, 21 Jul 2026 09:10:08 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id C929C6B008A for ; Tue, 21 Jul 2026 09:10:07 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 177E9120158 for ; Tue, 21 Jul 2026 13:10:07 +0000 (UTC) X-FDA: 85012816854.01.903179F Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf13.hostedemail.com (Postfix) with ESMTP id 42D7A20010 for ; Tue, 21 Jul 2026 13:10:05 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ndYTPFQl; spf=pass (imf13.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1784639405; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=se6gqaDgEIcoWq2sYffaHDfDYwxn+PTKjFhdFrseKmA=; b=0Re9rRG/wxnrUR13ndUeugCSo3kXprErByfolTEXtO5paUtGHoGJXfG00hd0iinQGRUlKU 6pIaIacOypQFjLK5+OkI5h8gsHy7UEswc4yTDDcpwj3uRlgRKkP2/9wIcZLhr7p+68qr5L NsvaxAdGWaLvZ5pF6Nq4zN4vjfMWRSo= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=ndYTPFQl; spf=pass (imf13.hostedemail.com: domain of vbabka@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1784639405; b=WR4PDD8xdugOQo7O7f+VkXoFdlUAn8J0525s7UEULVIlvdTNCM+vHWrkoFGSJ3HDxnBZ9i CaX8WpddxOY3z8dghqUH6rsSuURTvTDdmRjplN7mQSZ+3C6HwaYsOl+ghdtagboqWPEAT4 b9NkKfYHCl36zHPpLiWj+4YaJ3rwDgs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 13F3C40BE3; Tue, 21 Jul 2026 13:10:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88A6C1F000E9; Tue, 21 Jul 2026 13:09:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784639404; bh=se6gqaDgEIcoWq2sYffaHDfDYwxn+PTKjFhdFrseKmA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ndYTPFQlYdMidK4292aWniSBa3XvUSwM1icCePULSd+7ZUwX9ATRPlBVRx/Dkyi3I e0D0mjX4RuL6hndf4JYAiZltdfsKCavBJOHp2zPGKBDOJGS2MbbrfrOEfWniDFDRIl gAtimU9BenOKbbwd+L/DwIabjsJivI14QoojzIaeAQlsj438o9i+Pdk99Wlnt0/O5z Kau1jYbinm0F6qYROCIx5zsmjkSrB7DGpmhsRuzLB9XVVIY27L9jA5AQ1QNdGwBtdd SNgjIastSfaPtdCWFTcRKJmmkSbMWJmJhZRWj8Z1UYdJTRS/6WPE/i53CMyU3JojCi /IYAoBJFOBnFw== Message-ID: Date: Tue, 21 Jul 2026 15:09:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH slab/for-next v4 7/8] mm/slab: introduce kfree_rcu_nolock() Content-Language: en-US To: "Harry Yoo (Oracle)" , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alexei Starovoitov , Andrii Nakryiko , Puranjay Mohan , Amery Hung , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Pedro Falcato , Suren Baghdasaryan , Shengming Hu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, bpf@vger.kernel.org References: <20260720-kfree_rcu_nolock-v4-0-964e03c41a4e@kernel.org> <20260720-kfree_rcu_nolock-v4-7-964e03c41a4e@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260720-kfree_rcu_nolock-v4-7-964e03c41a4e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 42D7A20010 X-Stat-Signature: rpi1utrh9s6tyfcbfmcnwrmz1uof915o X-HE-Tag: 1784639405-591711 X-HE-Meta: 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 zbkthztL H81PfoELsQEGLJng9u4un4Ryo93VASo4Ig3wiV5Efzn1XxdtAZiVriQ5gSXGmYUMkb/SJ+MNuvh9pyTHnrVKPsItI+UDTwP/oXDWVHFuGfCjbUBkOvrw4I1L8bUPXZmM8EFU9732WcaEVvD4sq2ZrfiVI9aZKA9O8T9YBgKCb+TXcc+Ubue1vrm7PICPa1bK1LlwA7ACykNpL+iuN+vHuFwxYcNZbaUmKzesEC3y33darXFJq+oZnQtyNh3V5BfaJo3niNHEZRgrNEn4tLP4ZeIQ4VFviT9MWbuYSiCxbyW526fRknTqXakLC91JGW+dv1Yq6sCuyAolweLs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/20/26 14:44, Harry Yoo (Oracle) wrote: > Currently, k[v]free_rcu() cannot be called in unknown context since > it could lead to a deadlock when called in the middle of k[v]free_rcu(). > > Make users' lives easier by introducing kfree_rcu_nolock() variant, > now that kfree_rcu_sheaf() is available on PREEMPT_RT and > __kfree_rcu_sheaf() handles unknown context. > > kfree_rcu_nolock() falls back to the kvfree_rcu batching when sheaves > path fails. >From the code I would say it falls back to defer_kfree_rcu(), which is an irq_work that does kvfree_rcu batching? Otherwise the sentence would contradict the following: > In most cases, the sheaves path is expected to succeed > and it's unnecessary to add complexity to the existing kvfree_rcu > batching by teaching it how to handle unknown context. This talks about trying to perform the batching immediately without defering. > Since defer_kfree_rcu() can be called on caches without sheaves, move > deferred_work_barrier() and rcu_barrier() outside the branch in > kvfree_rcu_barrier_on_cache(). > > Signed-off-by: Harry Yoo (Oracle) Other than that and a comment correction below, LGTM. Reviewed-by: Vlastimil Babka (SUSE) > --- > include/linux/rcupdate.h | 19 +++++++++++++++++++ > mm/slab_common.c | 28 ++++++++++++++++++++++++++-- > mm/slub.c | 24 +++++++++++++++++++++++- > 3 files changed, 68 insertions(+), 3 deletions(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index ef5bb6981133..ce0fd401352e 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -1099,6 +1099,7 @@ static inline void rcu_read_unlock_migrate(void) > * In mm/slab_common.c, no suitable header to include here. > */ > void kvfree_call_rcu(struct kvfree_rcu_head *head, void *ptr); > +void kfree_call_rcu_nolock(struct kvfree_rcu_head *head, void *ptr); > > /* > * The BUILD_BUG_ON() makes sure the rcu_head offset can be handled. See the > @@ -1124,6 +1125,24 @@ do { \ > kvfree_call_rcu(NULL, (void *) (___p)); \ > } while (0) > > +/** > + * kfree_rcu_nolock() - a version of kfree_rcu() that can be called in any context. > + * @ptr: pointer to kfree for double-argument invocations. > + * @kvrhf: the name of the struct kvfree_rcu_head within the type of @ptr. > + * > + * Objects that are not allocated via kmalloc_nolock() are not supported. Is this true? If __kfree_rcu_sheaf() succeeds, rcu_sheaf is either flushed normally (call_rcu with rcu_free_sheaf()) or via the irq_work doing the same. The defer_kfree_rcu() fallback ends up doing a normal kvfree_call_rcu(). I don't see any path that ends up doing kfree_nolock(). Am I missing something? > + * kfree_rcu_nolock() supports 2-arg variant only. > + */ > +#define kfree_rcu_nolock(ptr, kvrhf) \ > +do { \ > + typeof (ptr) ___p = (ptr); \ > + \ > + if (___p) { \ > + BUILD_BUG_ON(offsetof(typeof(*(ptr)), kvrhf) >= 4096); \ > + kfree_call_rcu_nolock(&((___p)->kvrhf), (void *) (___p)); \ > + } \ > +} while (0) > + > /* > * Place this after a lock-acquisition primitive to guarantee that > * an UNLOCK+LOCK pair acts as a full barrier. This guarantee applies