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Thu, 26 Feb 2026 01:17:05 -0800 (PST) From: Qing Wang To: syzbot+3b5dd2030fe08afdf65d@syzkaller.appspotmail.com Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mathieu.desnoyers@efficios.com, mhiramat@kernel.org, rostedt@goodmis.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [trace?] WARNING in tracing_buffers_mmap_close (3) Date: Thu, 26 Feb 2026 17:16:57 +0800 Message-Id: <20260226091657.895403-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <699fc6d3.a00a0220.21906d.0073.GAE@google.com> References: <699fc6d3.a00a0220.21906d.0073.GAE@google.com> 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 #syz test diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 876358cfe1b1..07f5127c8255 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -248,6 +248,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node); int ring_buffer_map(struct trace_buffer *buffer, int cpu, struct vm_area_struct *vma); +void ring_buffer_map_user_mapped_inc(struct trace_buffer *buffer, int cpu); int ring_buffer_unmap(struct trace_buffer *buffer, int cpu); int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu); #endif /* _LINUX_RING_BUFFER_H */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f16f053ef77d..59516b89e612 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -7310,6 +7310,30 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu, return err; } +/** + * ring_buffer_map_user_mapped_inc - Increment user_mapped counter for VMA duplication + * @buffer: The ring buffer + * @cpu: The CPU of the ring buffer to increment + * + * This is called when a VMA is duplicated (e.g., on fork()) to increment + * the user_mapped counter without remapping pages. + */ +void ring_buffer_map_user_mapped_inc(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return; + + cpu_buffer = buffer->buffers[cpu]; + + guard(mutex)(&cpu_buffer->mapping_lock); + + if (cpu_buffer->user_mapped) + __rb_inc_dec_mapped(cpu_buffer, true); +} +EXPORT_SYMBOL_GPL(ring_buffer_map_user_mapped_inc); + int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 23de3719f495..b2ab95ed8d41 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8213,6 +8213,14 @@ static inline int get_snapshot_map(struct trace_array *tr) { return 0; } static inline void put_snapshot_map(struct trace_array *tr) { } #endif +static void tracing_buffers_mmap_open(struct vm_area_struct *vma) +{ + struct ftrace_buffer_info *info = vma->vm_file->private_data; + struct trace_iterator *iter = &info->iter; + + ring_buffer_map_user_mapped_inc(iter->array_buffer->buffer, iter->cpu_file); +} + static void tracing_buffers_mmap_close(struct vm_area_struct *vma) { struct ftrace_buffer_info *info = vma->vm_file->private_data; @@ -8232,6 +8240,7 @@ static int tracing_buffers_may_split(struct vm_area_struct *vma, unsigned long a } static const struct vm_operations_struct tracing_buffers_vmops = { + .open = tracing_buffers_mmap_open, .close = tracing_buffers_mmap_close, .may_split = tracing_buffers_may_split, };