From nobody Fri Sep 25 23:09:25 2026 Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A7A60525A60 for ; Mon, 7 Sep 2026 19:26:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.72 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788809211; cv=none; b=fiuyDCMT1iNvnG+ZTXZScgwrGFTrc+M4EDw3DNbmdGVIBZPV2imxETyAVVuBoD91VxbEGUWz8vJWT7tDYhx0VAdw7Lm1iucVIDXp1WVrXLAL2PLHOWehUpM0DsSHKBKpmlGfM7nsgVeToQbL8mhm+7ogLa5V8y34tc3GF8onHZQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788809211; c=relaxed/simple; bh=VV2UYtfj14QiFFoEBe2SgvinoxBkc3CLTdw0RZkYt4A=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=CwFe5QRQCbPVs4OHU3Hdnyc7nFDeXjBZDI18zXdN7qjFrMwZjkNC3QcGMe3X9ErN/nnl9ObLhR1vfy0n9VRfYglECrSof1FvQ5MvhJBW/xefK+DkfL0brbJW3TLI7c7hkfvzQDzf3rzGNfU8xPSJBYXkLBhRYVMTX9maVHNHL5w= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=JUuUwpRn; arc=none smtp.client-ip=209.85.128.72 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--vdonnefort.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="JUuUwpRn" Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-49ccb223bceso21749375e9.0 for ; Mon, 07 Sep 2026 12:26:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1788809207; x=1789414007; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=cOfeCPGjKhu5LNIU7QtSslcaAEx2w8+cq9M/aU9GG/0=; b=JUuUwpRnyvtvnhsicXI2LmAs/KYxwYoLDWO7P+B4s1yNxP5yX6GWvTLorTJM7vbgwB uVVuWQUjiB1/EgREhCtKRv2k9VVH6HOwB2JsP1TNcxSoNLmQWaq+vvQLaPznDbaHL1R2 nMQqmwaiAiRCUsgPCPnQyVp7Apx/Eoxd4NEGWB/v1A+O9VYYXKHzIFjUmNFiuTaZQrVF ax9vRCAKfsR0IPg7bEqPdlRrbkC73uvsvni+D2M8j+sW1VqVEV7HECIYqwVhGdmgRGcW exRbV0VSGDc3NGC4pNNCci8+fY8CK3n4okcRgn/gDeVmdtjpPyVa4uY/m0moWeXEE5UJ YgXw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788809207; x=1789414007; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=cOfeCPGjKhu5LNIU7QtSslcaAEx2w8+cq9M/aU9GG/0=; b=VBAvp1VW6HJ2+qQRfc35IHqt6eZzTUxuk1l+DZyw/Z+Q6b9Gl3M2Wl1Qsntv7pdxbU DUcLcTLSjlCMblYZcP9tKCgImFvlCE+j1HfTq8vL/2JZHha8o+kCi2czTOyJfVaREzmr 52bRvs2LlLjKbsMDkUUqZoLX5aCA+eyi9eC3gboWs039XiigYAG6fLsv5hWwkpEYOJmI A57blwHwxtn/SoUzDmkHiUpbs1fQEk59I2uPLscY4vXsoMtDWzdRz9rsXivuBVzTobK5 fKWHXaUdiEibvLQhDQIsZ4D1LWOGgZwhBDVjz1q7qI4hM/kgnyzVn9k/LQonJIdu6dH6 kPlg== X-Forwarded-Encrypted: i=1; AKwUvBwRPvrrkQ4u/L7VqbOufkpydZ80/06kmMPLgycdSMDcSt1MRDEKazR1TufJ07pXAQrJSOwe2g4NuZlnne4=@vger.kernel.org X-Gm-Message-State: AFuF++mwKAXNKZFuJVyDMXsLTxmb2xL4LX2rayttuc6qsNEAFKoHB+kw tR+YGdT5kigPk/zFXQa4Rt4MX9702haZbyAJderrdpiSuysVpxky3C1KnIjz8dvMmFxXB6viT8E DisQEs9mHy0DT6U4kVhpHTQ== X-Received: from wmcu4.prod.google.com ([2002:a7b:c044:0:b0:490:b475:af08]) (user=vdonnefort job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:4fd6:b0:49b:4eb6:6ffd with SMTP id 5b1f17b1804b1-49d1754ecbfmr30403525e9.5.1788809206748; Mon, 07 Sep 2026 12:26:46 -0700 (PDT) Date: Mon, 7 Sep 2026 20:26:42 +0100 In-Reply-To: <20260907192643.42513-1-vdonnefort@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260907192643.42513-1-vdonnefort@google.com> X-Mailer: git-send-email 2.55.0.979.g7e5102b832-goog Message-ID: <20260907192643.42513-2-vdonnefort@google.com> Subject: [PATCH v1 1/2] tracing/remotes: Account for ring buffer page header in size calculation 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" trace_buffer_desc_size() and trace_remote_alloc_buffer undercount the required pages because every ring buffer page contains a header (BUF_PAGE_HDR_SIZE). Account for that header to ensure allocated remote ring buffers aren't smaller than requested by the user. While at it, ensure those functions catch nr_pages overflow. Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index afc7daa6ee7d..7a1a92f87650 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -8,6 +8,8 @@ =20 #include =20 +#include + struct trace_buffer; struct ring_buffer_iter; =20 @@ -281,9 +283,14 @@ static inline struct ring_buffer_desc *__first_ring_bu= ffer_desc(struct trace_buf =20 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 + max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; 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 75fa1ffc4c96..2e0fdbb730b7 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)); - unsigned int nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE), 2UL) = + 1; struct ring_buffer_desc *rb_desc; int cpu, ret =3D -ENOMEM; + unsigned int nr_pages; + + if (min_desc_size =3D=3D SIZE_MAX) + return -E2BIG; =20 if (desc_size < min_desc_size) return -EINVAL; @@ -991,6 +994,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc = *desc, size_t desc_size, desc->struct_len =3D min_desc_size; =20 rb_desc =3D __first_ring_buffer_desc(desc); + nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE)= , 2UL) + 1; =20 for_each_cpu(cpu, cpumask) { unsigned int id; 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charset="utf-8" The codebase scatters hardcoded minimum page limits across multiple places. Introduce RING_BUFFER_MIN_NR_PAGES and rb_size_to_nr_pages() to formalize the requirement of two pages in a ring buffer. Remote and persistent ring buffers must account for the reader page. Signed-off-by: Vincent Donnefort diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 7a1a92f87650..a9401b8ebc72 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -99,6 +99,13 @@ 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 @@ -281,10 +288,15 @@ static inline struct ring_buffer_desc *__first_ring_b= uffer_desc(struct trace_buf return (struct ring_buffer_desc *)(&desc->__data[0]); } =20 +static inline unsigned long __ring_buffer_size_to_desc_pages(size_t size) +{ + /* Takes into account the reader page */ + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), RING_BUFFER= _MIN_NR_PAGES) + 1; +} + static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned i= nt nr_cpus) { - unsigned long nr_pages =3D - max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + unsigned long nr_pages =3D __ring_buffer_size_to_desc_pages(buffer_size); struct ring_buffer_desc *rbdesc; =20 /* Capped by ring_buffer_desc::nr_page_va */ diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 9c03a555a6ba..88e39d98332a 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_size_to_nr_pages(struct trace_buffer *buffer, unsi= gned 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_size_to_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_size_to_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_size_to_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); =20 cpu_buffer->nr_pages_to_update =3D nr_pages; =20 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)); diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 2e0fdbb730b7..0d90e02b1f4b 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -994,7 +994,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc = *desc, size_t desc_size, desc->struct_len =3D min_desc_size; =20 rb_desc =3D __first_ring_buffer_desc(desc); - nr_pages =3D max(DIV_ROUND_UP(buffer_size, PAGE_SIZE - BUF_PAGE_HDR_SIZE)= , 2UL) + 1; + nr_pages =3D __ring_buffer_size_to_desc_pages(buffer_size); =20 for_each_cpu(cpu, cpumask) { unsigned int id; --=20 2.55.0.979.g7e5102b832-goog