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b=RQssEgH8hHQ3F/Ij4GfslTLOAzgu+xn6hYeL9SpJucaJaSHmY1jEL+79ubRLV7ZCr aoe1Wd3i+Bu6YSVO/DLLVwlPCTvhE6hWNQ6QXQkiae72t9I57cR5szMQ/FBfG6ZOzz 7QOEImnHtsA5QS26mTMHd+IVG4oVgUyTHq3ZHyLY03MJSbvEteZj36hKV33jPux70w umYqOq3cy+mZinIEm6MkPN89bzt7SXR97PTEPla5zgf6W7SJVjxjSwBciWe9QZZaVZ i6I6QrALvC1h+UUurDWi29Z4irEHTdD5K5woaSGqbWrVpSctRm4WZra9k6xPJuCQ8S gBRunH7f/sbhA== Message-ID: Date: Thu, 5 Mar 2026 18:00:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [GIT PULL] tracing: Fixes for 7.0 To: Linus Torvalds , Steven Rostedt , Jason Gunthorpe , Leon Romanovsky Cc: Masami Hiramatsu , Mathieu Desnoyers , Huiwen He , Jerome Marchand , Qing Wang , Shengming Hu , Linux-MM , linux-rdma References: <20260305103941.11f1b27d@gandalf.local.home> 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: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 752D720005 X-Stat-Signature: ykckwyatd8r3wu1pytxthtaujtqe9wos X-Rspam-User: X-HE-Tag: 1772730028-105642 X-HE-Meta: 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 fHyXI2rY G/zzYdkPOIbRS6/c/BcipyuVxkfz4LYIsczD18LD0av/veY2Tm5bMP2ZYe47H4JFBgFVXI2y8rPfKYZW/IHo4qmesxED497zZVsi7nMJokOdGRYV8EkFvUEb4Bs/e9mtvqmBjf+1//OTf6VM3akMunh2AmSaG6fPOs9zax29j+XAqAEr2H4PI09npMgKVyXXXjLOMvzJXOqrGQfREXOeJaHpu/O3MIz6CIPff/gXiEH3HlhfzUedCQU7H6RzkiS/DrytXOpdC2AQhdJfO7ObdwdJ/8JAQxthSaokQ6FtWm4uyLDpc4NTTguBt1pn7zEWk3XV8 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/5/26 17:44, Linus Torvalds wrote: > [ Adding linux-mm and the rdma people ] > > On Thu, 5 Mar 2026 at 07:39, Steven Rostedt wrote: >> >> - Fix accounting of the memory mapped ring buffer on fork >> >> Memory mapping the ftrace ring buffer sets the vm_flags to DONTCOPY. But >> this does not prevent the application from calling madvise(MADVISE_DOFORK). > > I wonder how many other things have this assumption. > > Now, many (most?) of the VM_DONTCOPY users set VM_IO too, because the > most common reason they don't want to be copied is that it's a special > mapping. > > And then madvise() does nothing. > > But I also get the feeling that the whole *reason* for MADV_DOFORK > existing in the first place simply doesn't exist any more. > > It was added two decades ago when as a hack for the rdma people who > wanted to mix fork (with COW) and concurrent DMA, which just didn't > work reliably because the COW would break either way. Yes. > > See commit f822566165dd ("[PATCH] madvise MADV_DONTFORK/MADV_DOFORK"). > > And that should just not be an issue any more thanks to how it's now > done with page pinning rather than with the old GUP interfaces. > There are still weird cases with O_DIRECT and concurrent fork, where we don't use FOLL_PIN just yet (I know, I know, ... all shaky). QEMU traditionally sets MADV_DONTFORK on guest RAM. One reason is to speed up fork(), because it doesn't need all the guest RAM in fork'ed child processes. > So while I've pulled the tracing fix, I get the feeling that people > should at least think about just making MADV_{DO,DONT}FORK go away. > > Now, Debian code search does show some users (libfabric, libibverbs), > and maybe they actually want the forking behavior for other reasons > too. > I suspect we cannot get rid of it that easily. But ... > But I get the feeling that maybe we should at least limit MADV_DOFORK > only to the case where the *source* of the DONTFORK was the user, not > some kernel mapping. ... that makes sense. Forbid toggling it on something that has VM_SPECIAL set, maybe. Or at least forbid re-enabling it for such mappings. -- Cheers, David