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 02673384CE5; Tue, 11 Aug 2026 15:12:44 +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=1786461166; cv=none; b=QRjAxCOHfLJvObqjCJ/hWuiCnQjHyhpiFgYTo/Wu22WwUE6AXGelbgj57of4v1ZvpBVUYqSQ4qcOZtySLJdU2dW98/GYn1LZtZ9ZuL2xx40YRER54gysgaec6IdYuEPqo2z9krNqLXJtpLab3fS5nZWFbVc2uuiUL2K/VPFH2C4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786461166; c=relaxed/simple; bh=v0dPlt+Aa4+ZqeZw/6bpu02tt94HRXGQVIZ5D96o5MU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QK7RA62KCxxE7qo2jOvbs0QB9S5ED+XE/6lF/FOFn2Tc1+LBFCOsl0bdR77gyL55/AGQ98+krgWr1ruzg1t4zi68joWlFl4eJbx8k5sFoKR+jgBY+SpFS4cKTFZCfj7y7ptzIOD5PYV3MQIQ8H2Ug5hx4+1lgoo9SDGGygsIsuw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jKA8YClY; 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="jKA8YClY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 481201F000E9; Tue, 11 Aug 2026 15:12:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786461164; bh=KjnbmQ0CjfvfCvabbRwgNKDlNYfwps6m9E+P6DWnXxQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jKA8YClY4dU0SZbFCX+nX9ALHXaAF20S0uGoTYSxg5w75bE1NwCY62evaVYkNAPu/ Bd/q7K9i9DO+b0WWHVcv/gLPWt+Tt0ILRby87yQpaUOfNyGln0BebF1/izQX7MtON0 XrrKtaeU865KbkDPKqNQuCdLPhT7VFJ0Xm3pAS4zysFw/rBr5jENWy/V43y7bD4vdy 0C+G7U8jTrD3DrnXUJ3Xtgxj8IrQMetLRD+eE0GPzTAiHiFrQPf3PUYhpM0g+XSmDy vVP0rMGdX3CFM0/nCEhd5Kp9uWFI7VQuWrZ3aVqE5DsrnXuLz+3b5hBxB66NfXMFsH 358dILGA9WzYQ== Message-ID: <0b3ce586-a090-4741-b269-488106d33e3a@kernel.org> Date: Tue, 11 Aug 2026 17:12:36 +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] mm/mmu_notifier: Remove non_block_start/end() from notifier invocation To: David Woodhouse , Andrew Morton Cc: Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Jason Gunthorpe , Simona Vetter , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , =?UTF-8?Q?Christian_K=C3=B6nig?= , "Paul E. McKenney" , Paolo Bonzini , linux-mm@kvack.org, kvm@vger.kernel.org, linux-rt-devel@lists.linux.dev, linux-kernel@vger.kernel.org References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/11/26 10:58, David Woodhouse wrote: > From: David Woodhouse > > This effectively reverts commit ba170f76b69d ("mm, notifier: Catch > sleeping/blocking for !blockable") for the mmu_notifier call sites. > > The non_block_start/end() annotation causes the scheduler to complain > about *any* voluntary sleep in a non-blockable notifier. But that was > never the actual constraint. As Michal Hocko put it when the > annotation was first proposed (quoted in commit 312364f3534c > ("kernel.h: Add non_block_start/end()")), the OOM reaper "shouldn't > depend on any locks or sleepable conditionals" and checking for > sleepable context was "the best thing we could come up with that would > describe these demands at least partially". The real requirement is that the reaper > must not block on anything which may itself depend on memory > allocation (or on the dying mm) to make progress — which is why > spinning locks were always considered fine. I think it's conceptually more than that: "we mostly do care about it to make a forward progress". So yes, memory allocations are the obvious problem, but we also wouldn't want to wait on any lock that will be hard/impossible to get while reaping. Just take a look at what some mmu_notifier_range_blockable() users end up doing: they skip taking locks. [...] > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index 245b74f39f91..cd5d15cd646a 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -520,11 +520,7 @@ static int mn_hlist_invalidate_range_start( > if (ops->invalidate_range_start) { > int _ret; > > - if (!mmu_notifier_range_blockable(range)) > - non_block_start(); > _ret = ops->invalidate_range_start(subscription, range); > - if (!mmu_notifier_range_blockable(range)) > - non_block_end(); > if (_ret) { > pr_info("%pS callback failed with %d in %sblockable context.\n", > ops->invalidate_range_start, _ret, > @@ -591,14 +587,9 @@ mn_hlist_invalidate_end(struct mmu_notifier_subscriptions *subscriptions, > id = srcu_read_lock(&srcu); > hlist_for_each_entry_srcu(subscription, &subscriptions->list, hlist, > srcu_read_lock_held(&srcu)) { > - if (subscription->ops->invalidate_range_end) { > - if (!mmu_notifier_range_blockable(range)) > - non_block_start(); > + if (subscription->ops->invalidate_range_end) > subscription->ops->invalidate_range_end(subscription, > range); > - if (!mmu_notifier_range_blockable(range)) > - non_block_end(); > - } > } > srcu_read_unlock(&srcu, id); > } It's a bit odd. We have infrastructure to disallow blocking, and do so on multiple paths (just check for mmu_notifier_range_blockable() users where we skip taking mutexes, not performing memory allocations!), but now essentially allow blocking on some paths. That's just inconsistent. If we want different semantics, I think the whole thing should be re-thought: if blocking is suddenly allowed. -- Cheers, David