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 82E4BC44539 for ; Wed, 22 Jul 2026 10:06:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7F9A56B007B; Wed, 22 Jul 2026 06:06:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7AACE6B0088; Wed, 22 Jul 2026 06:06:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 671846B008A; Wed, 22 Jul 2026 06:06:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 2F6276B007B for ; Wed, 22 Jul 2026 06:06:00 -0400 (EDT) Received: from smtpin09.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id AFFBC1C081E for ; Wed, 22 Jul 2026 10:05:59 +0000 (UTC) X-FDA: 85015981638.09.C274D5C Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf21.hostedemail.com (Postfix) with ESMTP id 0AF7C1C0010 for ; Wed, 22 Jul 2026 10:05:57 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=l8yQoO+D; spf=pass (imf21.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 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=1784714758; 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=D6xRJg1cx2MApnHZbTatL/7rofeEJ41u17Yfn/n5svk=; b=1X3eNtHbniBVgdcVkb9Q+TpGFpxCPiGSLmhC7p50BV2dtbQ/+ynYW9wY0JreFqYwHt3cKt OhwCp4SMzsdIDdKDRy3g/dJHKI60FfkU9auc9KFWqnCPIAfpitrSiA9mcdznQB4G/9J++F KR67vxqGy3gWO4LodrmyrfG4qnEPzC4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1784714758; b=Byr5U39CHVOdM9HYr6MtHnOKEQPx1Nt29MtnTh2qR8qIrZmLhD0OcSWUOp8YgETBe3ljHi gi7Wu/M9maINF8Bsoghcv9KA6ns9v+55IVNNyW5WYtxulhbqgcpKM/5EGzaFaFOWmosXQ0 /b1R4gw23EKOsV8Vznk56m9wVI24M7s= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=l8yQoO+D; spf=pass (imf21.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 96967600DA; Wed, 22 Jul 2026 10:05:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 49D871F000E9; Wed, 22 Jul 2026 10:05:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784714757; bh=D6xRJg1cx2MApnHZbTatL/7rofeEJ41u17Yfn/n5svk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=l8yQoO+Dlue8vZ1yUqfeSgih4Rs9yNiQyqVpA7436Ssb9aTi4vw/bCvaoY28YmbhN nLUIuZnMQr4FsWHmbhjWhO5aO0g3mlmNM9IfG0Gj8lINAdf14fcSQ+wlh2m5vLg0gZ 8KMR6onERgLKAlrQfNIDBFCZxcA+z8KS4SjAJvBXKWCJRgD6dQ8FPKhYSy9W0mZ/ru 1VCvvamIr7Eu6raA8FcnBQe0BtPNHSqP4tYmdTzhYsN+hG0ne8bwgSbs6Mg9UGYyyN 4ir3qvSYcZtHmZWysW5Spo+OLmUs9gFWMBWojk7/VC7IXPC6Fr9oywbavW0lYX4HwW n9jfuNl8SxFmg== Message-ID: <8d67a924-9c1f-4e93-9e2a-4d71001167a2@kernel.org> Date: Wed, 22 Jul 2026 12:05:49 +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 , 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> <734ecdc6-f415-41d8-9357-7fc11379e4da@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: <734ecdc6-f415-41d8-9357-7fc11379e4da@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0AF7C1C0010 X-Stat-Signature: quoq71rbr51eopptyby7uurab9bhjx8z X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1784714757-724799 X-HE-Meta: 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 LzP1B4nm GwrI7AcoLsgKPjDhcCfiwEjQhlfmRlF5TTy9VoT0jimPlpG0tv3D2dESbJ9xzQ8Xi5QbnYJoFAx6x4TfXdrlj1WaD8+VVQgGSzxvw8cSdknpY2vctKLYC900NfGQ/gL/uJrR8CsRM847mcov8nd+lbI01ix2ziOQY+7/byg3xr9qPi9ye+0CF8BpAfdebAFFTKO/XgHpKYK/gcpaqQuMjlVvKmjhwr5kX9n9+w3u8bEcxnaXqAvzHz/J9dwp4z8knTQ8++oAW5Y+xecm6aWAbA8kOktk4xqoCImyZ2c4kXEuKfrYg+BjCjSpVuJtEWOaKn/l8Ir3Kt0f+InU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/22/26 10:15, Harry Yoo wrote: > On 7/21/26 10:09 PM, Vlastimil Babka (SUSE) wrote: >> 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? > > Indeed that was what I intended to say, but I messed up while > writing it :-) Will fix that. Thanks! >> 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. > > You mean the earlier sentence "kfree_rcu_nolock() falls back to the > kvfree_rcu batching when sheaves path fails", right? I was trying to point out how it contradicts the wording above. To be clear, with above fixed, this part is fine. >>> 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) > > Thanks! > >>> --- >>> 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? > > I added this limitation because I thought it doesn't make sense > to support this when we don't support large kmalloc and vmalloc in > unknown context. > > Perhaps too limiting than it should be though. Hmm right. Maybe we could just state that it handles all small kmalloc() and kmalloc_nolock() allocations without deferring as much as possible, but large k[v]malloc() allocations that end up being large_kmalloc() or vmalloc(), will also work but be always deferred? >>> + * 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 >