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[209.85.208.50]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b935ac704b0sm925409866b.22.2026.03.05.08.49.46 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2026 08:49:46 -0800 (PST) Received: by mail-ed1-f50.google.com with SMTP id 4fb4d7f45d1cf-660ea6ceb5aso3076899a12.0 for ; Thu, 05 Mar 2026 08:49:46 -0800 (PST) X-Forwarded-Encrypted: i=1; AJvYcCVhPFp8sKpycuToeapqwk6/sR4U6II3ZMLKgBKykGtFB2JswSz+4r1ubCkwzqxSgoKq4wrw4liDJw==@kvack.org X-Received: by 2002:a17:907:e10d:b0:b94:82e:55e7 with SMTP id a640c23a62f3a-b9409e75c5dmr122626266b.25.1772729083811; Thu, 05 Mar 2026 08:44:43 -0800 (PST) MIME-Version: 1.0 References: <20260305103941.11f1b27d@gandalf.local.home> In-Reply-To: <20260305103941.11f1b27d@gandalf.local.home> From: Linus Torvalds Date: Thu, 5 Mar 2026 08:44:27 -0800 X-Gmail-Original-Message-ID: X-Gm-Features: AaiRm537Jv2IcupKWNVngREUNm8d0KvSSjwd0obOsEpercpOSBsTAHZ8PEtbhj4 Message-ID: Subject: Re: [GIT PULL] tracing: Fixes for 7.0 To: Steven Rostedt , David Hildenbrand , Jason Gunthorpe , Leon Romanovsky Cc: Masami Hiramatsu , Mathieu Desnoyers , Huiwen He , Jerome Marchand , Qing Wang , Shengming Hu , Linux-MM , linux-rdma Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D703F10000F X-Stat-Signature: a5hqdeqo4sywdmnxiejz51rrqez4h5xg X-HE-Tag: 1772729388-972458 X-HE-Meta: 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 JgM2hsXY 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: [ 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. 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. 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. 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. Linus