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 2845A3AFD01; Wed, 17 Jun 2026 05:58:20 +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=1781675901; cv=none; b=TUr2YPzk4v7WKohbZoKyjf7L6cAIpHS2Bxn2irNExt7Y3X7ZFmPuvAPNp/FjNc2MDqu15j8rr4+77+jmNwBK8R+2/isLsH459DxbAH/zBycozFzZ9bo9144k2/fTcfjaQT2zpr7jYcs8yA8mZPniaTqG5YlwJxuI/+HIzSveMWc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781675901; c=relaxed/simple; bh=MKp+gQfP29ujZM4yIYrm7TJ0istjf6qopuT84uY3M/8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JztmYO4dEN9xB+GsgUoQkY7BeuD6oHU6spbFP9VinpWP+q6v6FV6PIMzzdrKNmcB7lN1x+svLeC2hYzCNKF0ET8jwqrx6ARFcv22MCrGvDaeqmwtNvzgZozKnfiRyLdo0Rsgz0iCIwAf7QjUarEZWDNAC+ge77G6cTv/si16y08= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RNB97Kz1; 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="RNB97Kz1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2DFC01F000E9; Wed, 17 Jun 2026 05:58:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781675899; bh=z0WnoCTe/WZyehgOrexh6SFggV7BqrfLheqjX/wcWBQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=RNB97Kz10Ao2R5CDg1QEMage+MHmk+FqZV1XZM+AotUPoZ7KQ0Z5T+pzTAbTnxBw5 Akfag50v5nhbjm1byNozw58F4ZlGMykbL+FJ/uhH0h4DMspxgDIlxOYxE3JLkSpc/h OCP+LwIwBY+uKtRjaZJTOxm/z8Iwe+7J2ylF2sIUs5MHx176pLyLiqq26IU8y11/db PO5luUTpvTYJ4KwMD7OwhbSyZDFDTVGH+XZalYYyH0zD0z+iXWrvKWqMifdoSP6UTm LtYwV5u6eqmFQXcGTCLD11o+wFeHPn4nIe/syIXpjCIOXx5om/rGxZpv14tdjXMhsl i7aerDDOvFFEg== Message-ID: Date: Wed, 17 Jun 2026 07:58:12 +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 for-next v3 3/9] mm/slab: handle the !allow_spin case in kfree_rcu_sheaf() 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 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: <20260615-kfree_rcu_nolock-v3-0-70a54f3775bb@kernel.org> <20260615-kfree_rcu_nolock-v3-3-70a54f3775bb@kernel.org> <4d7ebcd5-f3b7-4c73-94f1-b7d3ac12a521@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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/17/26 07:32, Harry Yoo wrote: >> Here we would get a sheaf with kmalloc_nolock() so that's ok even if it's >> later freed by someone else by kfree(), right. >> >>> + } >>> + >>> + empty = alloc_empty_sheaf(s, gfp, alloc_flags); >>> >>> if (!empty) >>> goto fail; >>> >>> if (!local_trylock(&s->cpu_sheaves->lock)) { >>> - barn_put_empty_sheaf(barn, empty); >>> + __free_empty_sheaf(s, empty, allow_spin); >> >> Well we could still use the barn with allow_spin == true. > > Initially I did > > if (!__barn_put_empty_sheaf(barn, empty, allow_spin)) > __free_empty_sheaf(s, empty, allow_spin); > > but I ended up just calling __free_empty_sheaf() because it's > pretty rare to hit... no strong opinion though. Yeah we can leave it simpler as it's rare. >> But more crucially, here we might be freeing with kfree_nolock() a sheaf >> from the barn previously allocated with kmalloc()? > > Well, we don't release and reacquire the local lock when we got an empty > sheaf from the barn, so it doesn't free the sheaf from the barn? > > That was indeed very subtle and I got confused :D. > > When we free a sheaf in this function, it's always allocated in current > context? Indeed! It's fine then. >> Maybe we need to track if it's the case and defer-free it or something. >> >> Also maybe there could be a wrapper kfree_maybe_nolock() (~better name?) >> That means "I want to kfree safely in kfree_nolock() context something that >> MIGHT have been kmalloc()" >> And maybe depending on the debugging options that make kmalloc() -> >> kfree_nolock() incompatible, if those are not enabled, it wouldn't have to >> defer, but proceed normally? > > But I really like the idea of supporting kmalloc() -> kfree_nolock(), > and I think it's worth exploring that. At least my confusion potentially lead to something good then :) > Thanks! >