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Thu, 26 Feb 2026 19:07:46 -0800 (PST) From: Qing Wang To: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, mhiramat@kernel.org, syzbot+3b5dd2030fe08afdf65d@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, wangqing7171@gmail.com Subject: Re: [syzbot] [trace?] WARNING in tracing_buffers_mmap_close (3) Date: Fri, 27 Feb 2026 11:07:37 +0800 Message-Id: <20260227030737.1089041-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260226115229.7111b070@gandalf.local.home> References: <20260226115229.7111b070@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-Transfer-Encoding: 8bit On Fri, 27 Feb 2026 at 00:52, Steven Rostedt wrote: > OK, so the issue is that the ring buffer was mapped, then the process that > mapped it forked duplicating the mappings. And then on exit (or unmap), > the first one to unmap the buffer will cause the ring buffer to think it > was fully unmapped causing the next one to unmap to trigger the error. > > > > + */ > > +void ring_buffer_map_user_mapped_inc(struct trace_buffer *buffer, int cpu) > > Let's call this ring_buffer_map_dup() to be consistent with ring_buffer_map(). > > inc would expect a dec, but dup() is more of what it is doing. > > > +{ > > + struct ring_buffer_per_cpu *cpu_buffer; > > + > > + if (!cpumask_test_cpu(cpu, buffer->cpumask)) > > + return; > > I wonder if this fails we should warn. As it should never be called unless > it was successfully mapped. > > > + > > + cpu_buffer = buffer->buffers[cpu]; > > + > > + guard(mutex)(&cpu_buffer->mapping_lock); > > + > > + if (cpu_buffer->user_mapped) > > + __rb_inc_dec_mapped(cpu_buffer, true); > > Probably should also warn if user_mapped is not set. Again, this should not > ever not be mapped if we get here. > > -- Steve Thanks for your suggestion. I sent a patch [0] and looking forward to your review. [0] https://lore.kernel.org/all/20260227025842.1085206-1-wangqing7171@gmail.com/ -- Best regards, Qing