From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 57CE33CF032; Fri, 1 May 2026 19:25:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777663530; cv=none; b=rYwGq+D9Dyx/4wa+0yqMl/bB/Lbr/2U6DX4r6emD0RrZMDGoEBy0X/IoaNvS6mEK7cw+oeMIXmYSViwyyKKl+HX2xL1VhoZDBTCD//y6pe/JlMjthA3oIfYHWTwaHnz5Fhk264vhUsHsvF9GK9LdeHSAlvTJgPRVz4voQ5yhsqw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777663530; c=relaxed/simple; bh=cynpdO+A6ieLH/h1ooFdUpbXEvoHioh79RIx3hzXzec=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lObc6owSLQyAn9ft63AXSfB3i+mqNt4WyfxGn+YC/DnHHfJqVtpA7+pZzXq7XR+tyFbxywgX3OPhnUvSf6ye68GqXS2REaLFEQR/9j6xZ688OzCc9cdou6k+pI+jKmYXRvbm7CM8/pTTKAwsvEmP+7APwi2ZDdw/gIf5cQYwXD4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WGLAmB26; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WGLAmB26" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1817CC2BCB4; Fri, 1 May 2026 19:25:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777663530; bh=cynpdO+A6ieLH/h1ooFdUpbXEvoHioh79RIx3hzXzec=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WGLAmB26o3fkD3UOKmk2RR8qmgItfkFPy1kHaO3qqCKRyNhbHBRjPY/M3rxUkmGoF CSzBPLXr49HvAq46Lw62Lu3z9ZpsnQLKya4MHlujisZlHUwA3VL09uWa7Wad1hJ+fp +Mcr3f7NxB58K1b0ECc9dxtmMicWQtWCHfgj+Vi21gMCGnQjQUUKcHSgI/tUskKA+p idRV9QaSo9D/uCTVKcTdnlOPZsgTXI/htqPkqm74UmUSwL9H7slRCbEflKhJu9mprL /TIPS7TiJ0TC4Qt2j/DtQHMsFYoeokm+b1zIXKxVMTrVzAo9duhyIA3fRhxSNyXINo XVTMKpufHSYJA== Message-ID: Date: Fri, 1 May 2026 21:25:20 +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/madvise: preserve uprobe breakpoints across MADV_DONTNEED To: "Daniel Walker (danielwa)" , Jann Horn Cc: Oleg Nesterov , "Darko Tominac -X (dtominac - GLOBALLOGIC INC at Cisco)" , Masami Hiramatsu , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , "xe-linux-external(mailer list)" , "linux-kernel@vger.kernel.org" , "linux-trace-kernel@vger.kernel.org" , "linux-perf-users@vger.kernel.org" , "linux-mm@kvack.org" References: <20260429131522.4049054-1-dtominac@cisco.com> <889e4186-9f75-45d3-bd9a-1c90b218a635@kernel.org> 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 4/30/26 21:25, Daniel Walker (danielwa) wrote: > On Thu, Apr 30, 2026 at 05:22:18PM +0200, Jann Horn wrote: >> On Wed, Apr 29, 2026 at 11:11 PM Daniel Walker (danielwa) >> wrote: >>> >>> >>> Shouldn't there be some sort of compensation or notification for this, or is each person that >>> hits this suppose to just scratch their head and send a patch that's rejected? >> >> I guess we could add a pr_warn_once() that warns when >> madvise(MADV_DONTNEED) is called on a read+execute file mapping, Private mapping, yes. MADV_DONTNEED indeed interacts poorly here. uprobe registration indeed fails if VM_WRITE is set (valid_vma), but nothing stops the VMA from getting mprotect'ed later I guess, to allow for write access. We could try marking a VMA that has uprobes, to then pr_warn_once() of MADV_DONTNEED is done on such a VMA. It wouldn't sort out ptrace access. >> and/or (as David said) add an explicit note in the madvise() manpage >> about how that can interfere with software breakpoints and uprobes? I guess not just software breakpoints, but any modifications done by a debugger. I guess for read+execute file mapping we would expect these to be software breakpoints. > > It does feel like it's the debuggers problem. The application doesn't know it's > getting debugged. So the application does whatever it does. If GDB is debugging > an application it should assume there's a problematic madvise() call which will > hurt/stop the debugging from happening. It should endeavor to prevent that > from happening. There are options in userspace to prevent it from happening. I'm > sure madvise() is not the only thing GDB has to worry about w.r.t. screwing up > the debugging. > > Noting it in the man page seems reasonable. I assume the bigger problem here is that MADV_DONTNEED was used for memory reclaim, when in fact, it shouldn't be used for that. For shared mappings, the man page even documents: "MADV_DONTNEED might not lead to immediate freeing of the pages in the range. The kernel is free to delay freeing the pages until an appropriate moment.". MADV_PAGEOUT is better for reclaim, but it has its limitations when it comes to pages shared with other processes. -- Cheers, David