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Account for that header to ensure allocated remote ring buffers aren't smaller than requested by the user. The newly introduced helper __calc_nr_pages_ring_buffer_desc() can return a value that overflows the descriptor nr_pages field (32 bits). Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Signed-off-by: Vincent Donnefort --- include/linux/ring_buffer.h | 15 +++++++++++++-- kernel/trace/trace_remote.c | 2 +- 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index afc7daa6ee7d..11bffb6a142d 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -3,8 +3,9 @@ #define _LINUX_RING_BUFFER_H =20 #include -#include #include +#include +#include =20 #include =20 @@ -279,9 +280,19 @@ static inline struct ring_buffer_desc *__first_ring_bu= ffer_desc(struct trace_buf return (struct ring_buffer_desc *)(&desc->__data[0]); } =20 +/* + * Returns the number of pages for a ring_buffer_desc. The caller must ens= ure it + * does not overflow ring_buffer_desc::nr_page_va. + */ +static inline unsigned long __calc_nr_pages_ring_buffer_desc(size_t size) +{ + /* Takes into account the reader page */ + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; +} + static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned i= nt nr_cpus) { - unsigned int nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) = + 1; + unsigned long nr_pages =3D __calc_nr_pages_ring_buffer_desc(buffer_size); struct ring_buffer_desc *rbdesc; =20 return size_add(offsetof(struct trace_buffer_desc, __data), diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 75fa1ffc4c96..c17902e42ef1 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -980,7 +980,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc = *desc, size_t desc_size, const struct cpumask *cpumask) { size_t min_desc_size =3D trace_buffer_desc_size(buffer_size, cpumask_weig= ht(cpumask)); 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charset="utf-8" The number of pages per remote ring buffer is capped by ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to overflow that field would silently allocate a descriptor smaller than what was asked for. Return SIZE_MAX from trace_buffer_desc_size() on nr_page_va overflow. Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Signed-off-by: Vincent Donnefort --- include/linux/ring_buffer.h | 4 ++++ kernel/trace/trace_remote.c | 6 +++++- 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 11bffb6a142d..eac3e9080c3c 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -295,6 +295,10 @@ static inline size_t trace_buffer_desc_size(size_t buf= fer_size, unsigned int nr_ unsigned long nr_pages =3D __calc_nr_pages_ring_buffer_desc(buffer_size); struct ring_buffer_desc *rbdesc; =20 + /* Capped by ring_buffer_desc::nr_page_va */ + if (nr_pages > UINT_MAX) + return SIZE_MAX; + return size_add(offsetof(struct trace_buffer_desc, __data), size_mul(nr_cpus, struct_size(rbdesc, page_va, nr_pages))); } diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index c17902e42ef1..2d5bc423efca 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -980,9 +980,12 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc= *desc, size_t desc_size, const struct cpumask *cpumask) { size_t min_desc_size =3D trace_buffer_desc_size(buffer_size, cpumask_weig= ht(cpumask)); 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Fri, 11 Sep 2026 12:39:55 -0700 (PDT) Date: Fri, 11 Sep 2026 20:39:37 +0100 In-Reply-To: <20260911193937.602202-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260911193937.602202-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.1007.g17ff1f9808-goog Message-ID: <20260911193937.602202-4-vdonnefort@google.com> Subject: [PATCH v2 3/3] ring-buffer: Unify ring buffer minimum page calculations 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, Vincent Donnefort Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The codebase scatters hardcoded minimum page limits across multiple places. Introduce RING_BUFFER_MIN_NR_PAGES and rb_calculate_nr_pages() to formalize the requirement of two pages in a ring buffer. Signed-off-by: Vincent Donnefort --- include/linux/ring_buffer.h | 9 ++++++++- kernel/trace/ring_buffer.c | 32 +++++++++++++------------------ kernel/trace/simple_ring_buffer.c | 4 ++-- 3 files changed, 23 insertions(+), 22 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index eac3e9080c3c..e4370064273e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -98,6 +98,13 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned = long size, unsigned flag =20 void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *= size); =20 +/* + * A minimum of 2 pages ensures we can always swap a page out of the ring + * buffer. This does not account for the reader page or any other page + * containing meta data used by static ring buffers. + */ +#define RING_BUFFER_MIN_NR_PAGES 2UL + /* * Because the ring buffer is generic, if other users of the ring buffer g= et * traced by ftrace, it can produce lockdep warnings. We need to keep each @@ -287,7 +294,7 @@ static inline struct ring_buffer_desc *__first_ring_buf= fer_desc(struct trace_buf static inline unsigned long __calc_nr_pages_ring_buffer_desc(size_t size) { /* Takes into account the reader page */ - return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), RING_BUFFER= _MIN_NR_PAGES) + 1; } =20 static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned i= nt nr_cpus) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..7137781ab0b8 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -642,6 +642,11 @@ static __always_inline unsigned int rb_subbuf_max_data= _size(struct trace_buffer return rb_subbuf_capacity(buffer) - RB_EVNT_HDR_SIZE - sizeof(event->arra= y[0]); } =20 +static unsigned long rb_calculate_nr_pages(struct trace_buffer *buffer, un= signed long size) +{ + return max(DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)), RING_BUFFER_MI= N_NR_PAGES); +} + /** * rb_subbuf_start - Get the start address of a subbuffer * @buffer: A trace buffer @@ -2865,7 +2870,7 @@ static struct trace_buffer *alloc_buffer(unsigned lon= g size, unsigned flags, goto fail_free_buffers; =20 /* Need at least two pages plus the reader page */ - if (nr_pages < 3) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; =20 again: @@ -2877,7 +2882,7 @@ static struct trace_buffer *alloc_buffer(unsigned lon= g size, unsigned flags, ptr +=3D subbuf_size * nr_pages; } if (ptr > end) { - if (nr_pages <=3D 3) + if (nr_pages <=3D RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; nr_pages--; goto again; @@ -2900,13 +2905,10 @@ static struct trace_buffer *alloc_buffer(unsigned l= ong size, unsigned flags, if (nr_pages > rb_static_max_pages()) goto fail_free_buffers; =20 - if (nr_pages < 2) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES) goto fail_free_buffers; } else { - /* need at least two pages */ - nr_pages =3D DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - if (nr_pages < 2) - nr_pages =3D 2; + nr_pages =3D rb_calculate_nr_pages(buffer, size); } =20 cpumask_set_cpu(cpu, buffer->cpumask); @@ -3319,11 +3321,7 @@ int ring_buffer_resize(struct trace_buffer *buffer, = unsigned long size, mutex_lock(&buffer->mutex); atomic_inc(&buffer->resizing); =20 - nr_pages =3D DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages =3D 2; + nr_pages =3D rb_calculate_nr_pages(buffer, size); =20 if (cpu_id =3D=3D RING_BUFFER_ALL_CPUS) { /* @@ -7495,12 +7493,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer= *buffer, int order) } =20 /* Update the number of pages to match the new size */ - nr_pages =3D old_capacity * buffer->buffers[cpu]->nr_pages; - nr_pages =3D DIV_ROUND_UP(nr_pages, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages =3D 2; + nr_pages =3D rb_calculate_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); =20 cpu_buffer->nr_pages_to_update =3D nr_pages; =20 @@ -8095,7 +8089,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hli= st_node *node) } /* allocate minimum pages, user can later expand it */ if (!nr_pages_same) - nr_pages =3D 2; + nr_pages =3D RING_BUFFER_MIN_NR_PAGES; buffer->buffers[cpu] =3D rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_b= uffer.c index 49913bb0057a..abfaf9bee12e 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -383,8 +383,8 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu= *cpu_buffer, void *page; int i; =20 - /* At least 1 reader page and two pages in the ring-buffer */ - if (desc->nr_page_va < 3) + /* At least RING_BUFFER_MIN_NR_PAGES and 1 reader page */ + if (desc->nr_page_va < RING_BUFFER_MIN_NR_PAGES + 1) return -EINVAL; =20 memset(cpu_buffer, 0, sizeof(*cpu_buffer)); --=20 2.55.0.1007.g17ff1f9808-goog