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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-483bfba9a5esm144533085e9.4.2026.02.27.07.16.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Feb 2026 07:16:54 -0800 (PST) Date: Fri, 27 Feb 2026 15:16:50 +0000 From: Vincent Donnefort To: Steven Rostedt Cc: Qing Wang , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, syzbot+3b5dd2030fe08afdf65d@syzkaller.appspotmail.com Subject: Re: [PATCH] tracing: Fix WARN_ON in tracing_buffers_mmap_close Message-ID: References: <20260227025842.1085206-1-wangqing7171@gmail.com> <20260227101002.614add75@gandalf.local.home> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260227101002.614add75@gandalf.local.home> On Fri, Feb 27, 2026 at 10:10:02AM -0500, Steven Rostedt wrote: > On Fri, 27 Feb 2026 10:41:17 +0000 > Vincent Donnefort wrote: > > > > Hum, not sure this is entirely correct. We do set VM_DONTCOPY when creating the > > > mapping (see __rb_map_vma). So AFAICT ->open() is not called in this situation (see > > > dup_mmap()) > > > > Ah right, Syzkaller is using madvise(MADVISE_DOFORK) which resets VM_DONTCOPY. > > Hmm, > > So this means user space can override the DONTCOPY? Can this cause bugs > elsewhere that DONTCOPY is used? Indeed, user space can clear DONTCOPY... unless we also set VM_IO. > > -- Steve