From nobody Mon Sep 28 06:32:05 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B07FE38F927; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676804; cv=none; b=ZFru+ywJM9ri3t9KSxo8Hs8X0ctFGuylqUYJ0FM7eh72l3V3BygYP+EDhnqG50KZk3egVpVoJBvBjTSKOwGJvjEH5P9mrr65DEgebcImZopM/JDSxFcfJKCofrQMz0FJP0ZDsbSfN3WqOixhmJ7SBBkAUifpaavX2OaNvgukWZI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676804; c=relaxed/simple; bh=Hk2FkW8rrOnBJBWeKeJ/xKFWNuL2YXyPRMVyxIwDSzs=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=cFhP1qEN/wSt1EGwmjR7ulFOhsUqUsD6ae2k2TH0XAx2FAi/yDN0DwiqAvI25xoVLXciKEHcX4BS52iBkneEdBCbHay20Lq6+3qHQ+ZfbkSSkCDzARrfs62Iup2jEl++KhrNngPc/JkzMYk/2DOBwpBOQIwNzjdaa+d87xHQthE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vCrZMQMb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vCrZMQMb" Received: by smtp.kernel.org (Postfix) with ESMTPS id 68808C2BCFA; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1787676804; bh=Hk2FkW8rrOnBJBWeKeJ/xKFWNuL2YXyPRMVyxIwDSzs=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=vCrZMQMbPK163h1sYcPgL8fiOJaj2MqWShCJVcWuJV7CyNLjRkSSVh69I7Mi1aArP adzrKJsiu9ofCKLrvuoMvTEQhLyBZzlP5ujl7YotVBArU6nNwn7oJOUwnwM9onYl28 FCGNHmiTVd4DTEmgI5mpA+9jXRfhiVqxXvs3zQ3reiC4PvDE5HJ8HgktKFSrkzJtyr s1E09Z64mvaNU5UyjG/wngXpdrkeDR22xNRxcxMISbc5hSHo+vta/Dx2mQ4ByQJFaz wG8dglvafxbcXD8vb2pzIjkqgV2+urmUgEKjMJv9WwEEngSLIaFmjT98YqofEzb/3i m+Un8UmyivEXw== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4590FC61DBD; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) From: Ivan Immanuel Shaji via B4 Relay Date: Tue, 25 Aug 2026 12:52:49 -0400 Subject: [PATCH v2 1/2] tracing: Fix retry exhaustion in simple ring buffer reader swap 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="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260825-kernel-patch-1-v2-1-bb3461807a32@gmail.com> References: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> In-Reply-To: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> To: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Vincent Donnefort Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org, Ivan Immanuel Shaji X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787676803; l=1669; i=ivanimmanuel1234@gmail.com; s=20260825; h=from:subject:message-id; bh=0wlmuiqSThih8CNT0Jea/HbIHZ739kvpr2URRAfi46Y=; b=R2DpCEXju5XYQhQ2OyLBs0xLycXPVX5jRLVbIskDnXkcQD5sSsTRK67g0iwBxw7xpkTviX/o3 9ly37jhgzggAXm1tVCvEcC0k1OgHoBNUAtqzvrMvu7BgQznSAN4nOoP X-Developer-Key: i=ivanimmanuel1234@gmail.com; a=ed25519; pk=Wx8O3UUs3XneDkbqbOJJnlNdWSpEf2tWbTAoE7/vnqE= X-Endpoint-Received: by B4 Relay for ivanimmanuel1234@gmail.com/20260825 with auth_id=975 X-Original-From: Ivan Immanuel Shaji Reply-To: ivanimmanuel1234@gmail.com From: Ivan Immanuel Shaji simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. The current !retry test reverses both outcomes. It returns an error after a successful final replacement, leaving the link update complete but the reader bookkeeping unfinished. After a failed final replacement, it falls through and updates the head and reader pointers as though the replacement succeeded, which can corrupt the ring. Treat only a negative counter as exhaustion and return the documented -EBUSY error. Fixes: 34e5b958bdad ("tracing: Introduce simple_ring_buffer") Cc: stable@vger.kernel.org Assisted-by: LLM sparse Reviewed-by: Vincent Donnefort Signed-off-by: Ivan Immanuel Shaji --- kernel/trace/simple_ring_buffer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_b= uffer.c index f4642f5adda3..49913bb0057a 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -160,8 +160,8 @@ int simple_ring_buffer_swap_reader_page(struct simple_r= b_per_cpu *cpu_buffer) overrun =3D cpu_buffer->meta->overrun; } while (!simple_bpage_unset_head_link(last, reader, SIMPLE_RB_LINK_NORMA= L) && retry--); =20 - if (!retry) - return -EINVAL; + if (retry < 0) + return -EBUSY; =20 cpu_buffer->head_page =3D simple_bpage_from_link(reader->link.next); cpu_buffer->head_page->link.prev =3D &reader->link; --=20 2.53.0 From nobody Mon Sep 28 06:32:05 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B060937C930; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676804; cv=none; b=NrRztzsm0IMgWcLEy/LOBKhWBtvigWhu5G2qwhTIi1mgOHQyTmG01pLCH7oysLIZF2DThZBsCfS6B5F8fC1FMQDShdfpsR1gR2C4TrgdfwElrqwTipqf56I5h/I30an1eWM5QLtAI+74IcTxEk5BX3oHFg1JwcyTfjKOvJqOC4s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676804; c=relaxed/simple; bh=UtsO0Gokd/pGWTPuvAgNuOYh/Tb/GGTu3I5Ny6vLdtk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=SHUBv7/c5jXPmgha1XASmJ+Re8vR3hnpZpKQhDK4BLy1NEUF0WjPehKWO4QgU3/UDV9LN3g2Vat/URlTuK8ZNclQxKxxbX2BfQ8exkyEpQpZCsbII53HIyNUEoDMbisFrDC3AT0Gi/Ig+w429BnArHdb6Ul7kq7dxKexMZ4wCNc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qHY10SNL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qHY10SNL" Received: by smtp.kernel.org (Postfix) with ESMTPS id 71B30C2BCFB; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1787676804; bh=UtsO0Gokd/pGWTPuvAgNuOYh/Tb/GGTu3I5Ny6vLdtk=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=qHY10SNL5E0cZuuqOfLziGE9cQnjOcWWldGqdvSGYVSqCCcY1ltc23aeM1jKX2TZv GGqncvAnJh/1YoNg06yt7KmUoIFu8ppaMttMBBVZaS+Oy68DnQlMtnXFJGV7WXZOW8 Ez6vycZBp2ZZBdHbQYbJUKVxsiJ25Sosm5ge6VDEXX9QWc1+DO8vqxvpdoI2XurrOI isnQkL+NCbjHQPRWhPnYJS+XULSY+8zf1q9XOWpG9iS2Fn++TyPUwJPf5Tzw7qaEyz BQnNJTc6aG7KiQP2Eu13aqL+g4ucwiDTq0f1oiX9jaHkO4WKcV3jPYnyfCmxD4hC4G h7ztQf6q/yKpQ== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54AA9C61DBE; Tue, 25 Aug 2026 16:53:24 +0000 (UTC) From: Ivan Immanuel Shaji via B4 Relay Date: Tue, 25 Aug 2026 12:52:50 -0400 Subject: [PATCH v2 2/2] ring-buffer: Stop remote reader update when page swap fails 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="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260825-kernel-patch-1-v2-2-bb3461807a32@gmail.com> References: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> In-Reply-To: <20260825-kernel-patch-1-v2-0-bb3461807a32@gmail.com> To: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Vincent Donnefort Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org, Ivan Immanuel Shaji X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787676803; l=1736; i=ivanimmanuel1234@gmail.com; s=20260825; h=from:subject:message-id; bh=LNL2ffJz8llLBy4R+x3iJYnTiH9lI0OfoRC4hz5apiw=; b=QJKEN/5hZjtWkMBMH/i//qnraPVZXGGRR6NaiSx4oqq97BchClSXatijJio6RkkoNRwlXovwC VCPjsCR5Th5DCwPrek+JH9QfoB5TYU6QQAzsDO/Dc1D+/dccnIybkcB X-Developer-Key: i=ivanimmanuel1234@gmail.com; a=ed25519; pk=Wx8O3UUs3XneDkbqbOJJnlNdWSpEf2tWbTAoE7/vnqE= X-Endpoint-Received: by B4 Relay for ivanimmanuel1234@gmail.com/20260825 with auth_id=975 X-Original-From: Ivan Immanuel Shaji Reply-To: ivanimmanuel1234@gmail.com From: Ivan Immanuel Shaji The remote swap_reader_page callback can return -EBUSY when the writer moves the head before the remote catches it, particularly during an event storm on a small buffer. __rb_get_reader_page_from_remote() currently warns about that failure but continues with the unchanged reader ID and rearranges the local page list as though the swap succeeded. Handle the callback failure as a recoverable error. Report it with pr_warn_ratelimited() and return NULL. Callers already handle a NULL reader page as a failed attempt. This avoids splicing the same page as both the previous and new reader without flooding the log under contention. Fixes: 2e67fabd8b77 ("ring-buffer: Introduce ring-buffer remotes") Cc: stable@vger.kernel.org Assisted-by: LLM sparse Signed-off-by: Ivan Immanuel Shaji --- kernel/trace/ring_buffer.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3c3ed639923d..b0963ac6fd16 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5805,8 +5805,11 @@ __rb_get_reader_page_from_remote(struct ring_buffer_= per_cpu *cpu_buffer) =20 prev_reader =3D cpu_buffer->subbuf_ids[cpu_buffer->meta_page->reader.id]; =20 - WARN_ON_ONCE(cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, - cpu_buffer->remote->priv)); + if (cpu_buffer->remote->swap_reader_page(cpu_buffer->cpu, + cpu_buffer->remote->priv)) { + pr_warn_ratelimited("Remote reader page swap failed\n"); + return NULL; + } /* nr_pages doesn't include the reader page */ if (WARN_ON_ONCE(cpu_buffer->meta_page->reader.id > cpu_buffer->nr_pages)) return NULL; --=20 2.53.0