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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4999d063a68sm26758815e9.2.2026.08.17.03.27.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Aug 2026 03:27:05 -0700 (PDT) Date: Mon, 17 Aug 2026 11:27:01 +0100 From: Vincent Donnefort To: rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org Cc: mathieu.desnoyers@efficios.com, kernel-team@android.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 2/2] ring-buffer: Improve nr_pages type Message-ID: References: <20260814154823.755406-1-vdonnefort@google.com> <20260814154823.755406-3-vdonnefort@google.com> 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-Disposition: inline In-Reply-To: <20260814154823.755406-3-vdonnefort@google.com> On Fri, Aug 14, 2026 at 04:48:23PM +0100, Vincent Donnefort wrote: > If ring_buffer_per_cpu::nr_pages is defined as unsigned long, it is > capped to 32-bits in a few places, limiting the operations possible on a > very large buffer. > > Make sure nr_pages is never capped to 32-bits (that includes nr_subbufs) > and reject a value over 32-bits for the user-mapped, persistent buffer > and remote buffer cases where the limiting factor is the shared > meta-data member for the number of pages/subbufs. > > While at it, make sure subbuf_size is 'unsigned int'. > > Signed-off-by: Vincent Donnefort > --- > kernel/trace/ring_buffer.c | 46 ++++++++++++++++++++++++-------------- > 1 file changed, 29 insertions(+), 17 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index ec13779922ff..ec127e2ad052 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -1669,7 +1669,7 @@ static void rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer) > * This is used to help find the next per cpu subbuffer within a mapped range. > */ > static unsigned long > -rb_range_align_subbuf(unsigned long addr, int subbuf_size, int nr_subbufs) > +rb_range_align_subbuf(unsigned long addr, unsigned int subbuf_size, unsigned long nr_subbufs) > { > addr += sizeof(struct ring_buffer_cpu_meta) + > sizeof(int) * nr_subbufs; > @@ -1679,13 +1679,12 @@ rb_range_align_subbuf(unsigned long addr, int subbuf_size, int nr_subbufs) > /* > * Return the ring_buffer_meta for a given @cpu. > */ > -static void *rb_range_meta(struct trace_buffer *buffer, int nr_pages, int cpu) > +static void *rb_range_meta(struct trace_buffer *buffer, unsigned long nr_pages, int cpu) > { > - int subbuf_size = rb_subbuf_size(buffer); > + unsigned int subbuf_size = rb_subbuf_size(buffer); > struct ring_buffer_cpu_meta *meta; > struct ring_buffer_meta *bmeta; > - unsigned long ptr; > - int nr_subbufs; > + unsigned long ptr, nr_subbufs; > > bmeta = buffer->meta; > if (!bmeta) > @@ -1731,7 +1730,7 @@ static void *rb_range_meta(struct trace_buffer *buffer, int nr_pages, int cpu) > /* Return the start of subbufs given the meta pointer */ > static void *rb_subbufs_from_meta(struct ring_buffer_cpu_meta *meta) > { > - int subbuf_size = meta->subbuf_size; > + unsigned int subbuf_size = meta->subbuf_size; > unsigned long ptr; > > ptr = (unsigned long)meta; > @@ -1746,8 +1745,8 @@ static void *rb_subbufs_from_meta(struct ring_buffer_cpu_meta *meta) > static void *rb_range_buffer(struct ring_buffer_per_cpu *cpu_buffer, int idx) > { > struct ring_buffer_cpu_meta *meta; > + unsigned int subbuf_size; > unsigned long ptr; > - int subbuf_size; > > meta = rb_range_meta(cpu_buffer->buffer, 0, cpu_buffer->cpu); > if (!meta) > @@ -1840,10 +1839,10 @@ static bool rb_meta_init(struct trace_buffer *buffer, int scratch_size) > * must be the same. > */ > static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu, > - struct trace_buffer *buffer, int nr_pages, > + struct trace_buffer *buffer, unsigned long nr_pages, > unsigned long *subbuf_mask) > { > - int subbuf_size = PAGE_SIZE; > + unsigned int subbuf_size = PAGE_SIZE; > unsigned long buffers_start; > unsigned long buffers_end; > int i; > @@ -2231,7 +2230,8 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer) > } > } > > -static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages, int scratch_size) > +static void rb_range_meta_init(struct trace_buffer *buffer, > + unsigned long nr_pages, int scratch_size) > { > struct ring_buffer_cpu_meta *meta; > unsigned long *subbuf_mask; > @@ -2417,7 +2417,7 @@ static void *ring_buffer_desc_page(struct ring_buffer_desc *desc, unsigned int p > } > > static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, > - long nr_pages, struct list_head *pages) > + unsigned long nr_pages, struct list_head *pages) > { > struct trace_buffer *buffer = cpu_buffer->buffer; > struct ring_buffer_cpu_meta *meta = NULL; > @@ -2545,7 +2545,7 @@ static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer, > } > > static struct ring_buffer_per_cpu * > -rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu) > +rb_allocate_cpu_buffer(struct trace_buffer *buffer, unsigned long nr_pages, int cpu) > { > struct ring_buffer_per_cpu *cpu_buffer __free(kfree) = > alloc_cpu_buffer(cpu); > @@ -2702,8 +2702,8 @@ static void rb_test_inject_invalid_pages(struct trace_buffer *buffer) > struct ring_buffer_cpu_meta *meta; > struct buffer_data_page *dpage; > unsigned long entry_bytes = 0; > + unsigned int subbuf_size; > unsigned long ptr; > - int subbuf_size; > int invalid = 0; > int cpu; > int i; > @@ -2773,8 +2773,8 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > struct ring_buffer_remote *remote) > { > struct trace_buffer *buffer __free(kfree) = NULL; > - long nr_pages; > - int subbuf_size; > + unsigned int subbuf_size; > + unsigned long nr_pages; > int bsize; > int cpu; > int ret; > @@ -2837,6 +2837,10 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > */ > nr_pages = (size - sizeof(struct ring_buffer_cpu_meta)) / > (subbuf_size + sizeof(int)); > + > + /* limited by ring_buffer_cpu_meta::nr_subbufs */ > + if (nr_pages > U32_MAX - 1) > + goto fail_free_buffers; > /* Need at least two pages plus the reader page */ > if (nr_pages < 3) > goto fail_free_buffers; > @@ -2869,6 +2873,10 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, > /* The writer is remote. This ring-buffer is read-only */ > atomic_inc(&buffer->record_disabled); > nr_pages = desc->nr_page_va - 1; > + > + /* limited by ring_buffer_desc::nr_page_va */ > + if (nr_pages > U32_MAX - 1) > + goto fail_free_buffers; > if (nr_pages < 2) > goto fail_free_buffers; > } else { > @@ -7421,8 +7429,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) > struct ring_buffer_per_cpu *cpu_buffer; > struct buffer_page *bpage, *tmp; > unsigned int old_capacity; > + unsigned long nr_pages; > int old_order; > - int nr_pages; > int psize; > int err; > int cpu; > @@ -7604,7 +7612,7 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer, > struct buffer_page **subbuf_ids) > { > struct trace_buffer_meta *meta = cpu_buffer->meta_page; > - unsigned int nr_subbufs = cpu_buffer->nr_pages + 1; > + unsigned long nr_subbufs = cpu_buffer->nr_pages + 1; > struct buffer_page *first_subbuf, *subbuf; > int cnt = 0; > int id = 0; > @@ -7834,6 +7842,10 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu, > /* prevent another thread from changing buffer/sub-buffer sizes */ > guard(mutex)(&buffer->mutex); > > + /* limited by trace_buffer_meta::nr_subbufs */ And actually I have realised the limiting factor is bpage::id which is only 30-bits. > + if (cpu_buffer->nr_pages > U32_MAX - 1) > + return -E2BIG; > + > err = rb_alloc_meta_page(cpu_buffer); > if (err) > return err; > -- > 2.55.0.691.gc56d675ccc-goog > -- Vincent