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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483b81986cdsm29112075e9.0.2026.02.24.01.43.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Feb 2026 01:43:10 -0800 (PST) Date: Tue, 24 Feb 2026 09:43:09 +0000 From: David Laight To: Christian Brauner Cc: Oleg Nesterov , Jann Horn , Linus Torvalds , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: pidfd && O_RDWR Message-ID: <20260224094309.591e7db1@pumpkin> In-Reply-To: <20260223-ziemlich-gemalt-0900475140e5@brauner> References: <20260223-work-pidfs-autoreap-v4-0-e393c08c09d1@kernel.org> <20260223-work-pidfs-autoreap-v4-2-e393c08c09d1@kernel.org> <20260223-ziemlich-gemalt-0900475140e5@brauner> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 23 Feb 2026 22:39:22 +0100 Christian Brauner wrote: > On Mon, Feb 23, 2026 at 08:21:02PM +0100, Oleg Nesterov wrote: > > On 02/23, Oleg Nesterov wrote: > > > > > > pidfd_prepare() does pidfs_alloc_file(pid, flags | O_RDWR) and "| O_RDWR" > > > makes no sense because pidfs_alloc_file() itself does > > > > > > flags |= O_RDWR; > > > > > > I was going to send the trivial cleanup, but why a pidfs file needs > > > O_RDWR/FMODE_WRITE ? > > > > > > Actually the same question about some anon_inode_getfile_fmode(O_RDWR) > > > users, for example signalfd.c. > > > > perhaps an accidental legacy from 628ff7c1d8d8 ("anonfd: Allow making anon > > files read-only") ? > > It was always a possibility that we would support some form of > write-like operation eventually. And we have support for setting trusted > extended attributes on pidfds for some time now (trusted xattrs require > global cap_sys_admin). > Isn't 'sending a signal' a write-like operation? David