From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 6D2EE21254B; Tue, 21 Jul 2026 13:10:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784639405; cv=none; b=pcIq1IO+W4tBDE73WCoAspPJPiZjDIIrwa/Qe8tZa+1SFsfG4eOVQhC/mngcnoHUE28NA20QB2zjMMHKX37Kn3AlMmI4aJHl2b3/LvYth1KE/a4+JYsoPMKgNQqeYQUjUU02K+BRsSWm8M8V5wY+BFvOqRJPOOcErzqq7Hw1nVY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784639405; c=relaxed/simple; bh=L7BxOMaKk8dhDd5wnsp0AmK9HHtUQZZe34ipil94oJc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Bi+eaA252HQx/YjmqiT4JA3N9IP9kRRT1i/Klt1eZRLM4eNtFANaa2m1FxFVizsfJ3ICPSFQhtrKyNKx73hrOooGiWijJSZxWtbDwDSgYz7zjrMkyCRhfNl8QCfmJ8IT5TIJm/F/BCS6myw4gdN75aXRBj1al4GU7m/XGq4Woss= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ndYTPFQl; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ndYTPFQl" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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