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 01A5036212D; Thu, 11 Jun 2026 08:51:25 +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=1781167886; cv=none; b=TdEHnC9XqZKrBp3dlzxsvebPpaAUIRiOKAIp+Z7sUtKGqFXJ5MuTk068YO4gMiAW8QX45lw6c3TBR161h0loYhQV8/Vw+/cJHSIWRjezey7k2yjTwpPqivBBLxXwwbT+qWnIqFWNBw3SZfOkYleg0WzOAduSNhdoamRY6ZijKfc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781167886; c=relaxed/simple; bh=m7ppkDDqCpZgZEYGPw1fKZ1D6F2/FkNGWTH8OlV4Els=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=R8h7ccfb3tdcX42omAVbNEOOyC32HbuBUavnHf/oOCEigI/fcgyrp8VlApv7U3ivrep3gG0AMzEtVtcUVatpURADL5FtY5tANDqRjRkH0BmAxC2rOmboMLEBvvB/8JN0JV1mjAFTFSthn39IhmiOu48dEI8p/GpliYZh3jg/twk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VLSc6bFy; 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="VLSc6bFy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4DDA1F00893; Thu, 11 Jun 2026 08:51:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781167885; bh=tKQY3q8LRG8SYeUWFL/Ai08b37v/C5UOx3jw/kl3HVc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VLSc6bFy8Nf4LrmeiH/AXvTLCsV4NmbpcD+RqmKowxdCB1XJ6GSorOidWsAd4Uc5T cseJqJ1r5/e3+o02SKnJt8sUffKyjuanvLaH/EHDaUBaQaIdx+11MPWKFNU54d+pJr eUnRU5ZW3nhYTCiK5cq6v0onacSYnkHWChRIcX/73nFH8qqhno503WbUOZwd5UxmyE 0nAlFbjS6CX0CfGZfd+aV+S83PbRSLb1lyVM/skhZY72WX3YAHAWmwmYSVIjAiYmST v9nTzgZbn48/SHfr/DDBNCgFZg3dCsAED04OD3TI6YTfAgfPIYnQMhDcN9IjKSEKOw QJ1/z6NJyo72Q== Message-ID: <3d6e1e47-efea-4f4f-889e-ce5a89cf808a@kernel.org> Date: Thu, 11 Jun 2026 10:51:20 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 05/16] mm/slab: introduce alloc_flags and SLAB_ALLOC_TRYLOCK Content-Language: en-US To: Harry Yoo Cc: Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Alexei Starovoitov , Andrew Morton , Johannes Weiner , Michal Hocko , Shakeel Butt , Alexander Potapenko , Marco Elver , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260610-slab_alloc_flags-v2-0-7190909db118@kernel.org> <20260610-slab_alloc_flags-v2-5-7190909db118@kernel.org> <7064a90e-4bf5-4be7-8b7f-a5a11dcee66f@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/11/26 08:40, Harry Yoo wrote: > Sashiko wrote [1]: >> Does this bypass the caller's gfp constraints for standard allocations? >> Looking at slab_alloc_node(), standard allocations now pass >> SLAB_ALLOC_DEFAULT into alloc_from_pcs(): >> - object = alloc_from_pcs(s, gfpflags, node); >> + object = alloc_from_pcs(s, gfpflags, SLAB_ALLOC_DEFAULT, node); >> This default flag means alloc_flags_allow_spinning() will unconditionally >> return true regardless of the gfp flags provided. > > Yes, but that's not used in _nolock path > as mentioned in patch 6 description :) > >> If a caller allocating under a raw spinlock intentionally strips >> __GFP_KSWAPD_RECLAIM (for example, by using __GFP_NOWARN) to prevent >> sleeping, > > That's a horrible hack (and hypothetical. Nobody should be stripping > __GFP_KSWAP_RECLAIM instead of using kmalloc_nolock(). That's purely > broken). Indeed this was never intended to work, and was just an unfortunate sideffect of the gfp flag reuse to implement kmalloc_nolock(). >> won't this allow the allocator to execute spin_lock_irqsave() >> on barn->lock or n->list_lock? >> >> On systems with preempt-rt enabled, a standard spinlock maps to a sleeping >> lock, so taking these locks in an atomic context could cause a scheduling >> while atomic panic. >> >> Since there is no nolock variant available for custom caches, do callers >> currently have any alternative mitigation? > > Well, RT kernels are not supposed to allocate meomry under a raw > spinlock (at least w/ allow_spin = true) Yep. > [1] > https://sashiko.dev/#/patchset/20260610-slab_alloc_flags-v2-0-7190909db118%40kernel.org >