From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f45.google.com (mail-wr1-f45.google.com [209.85.221.45]) (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 D15D73E49C8 for ; Tue, 25 Aug 2026 08:34:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.45 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787646869; cv=none; b=MpUkL9b3s/oVOo8/RQ+sZIhs4n4a7c2SZPZGJZ0ZdhcHl019psSKMhveXH8oZA0Ag7dCGrJ+dfnNHdL7mvYzgL/QA3v5hpdBF5YZftuccD5SCaYax21UcE1ZAeeL9Dpp+Ak7VdOid3DkuviKDKpWkD+nU01a0p9ZafroX3gJaxw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787646869; c=relaxed/simple; bh=Osz8dIVx9pcjDLZBVhUg7eExjzhfbTT9XPNOuGpP5Ys=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Mzz3AgJvWlo8yxQUCfSfi8i7MXsFT63074HeIxHBqpZZhfeEe6a5ueGZpf0x4wMMXXakn1lDPS9WEFLm0Yv+S+KrdjJSdKC/H1DjRAGdnUHjPDUZuj4HIBPYGb3oAfS5w7CDLu+ym1/MsAj25CSVitZtSfmJPw6+XLBCP9S90QM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=XcC/pSNe; arc=none smtp.client-ip=209.85.221.45 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=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="XcC/pSNe" Received: by mail-wr1-f45.google.com with SMTP id ffacd0b85a97d-472326ca506so2297683f8f.2 for ; Tue, 25 Aug 2026 01:34:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1787646866; x=1788251666; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=IVGtX9QFUX57YpBuir6YXJ5ojxTug80HJTjtVuCANHI=; b=XcC/pSNeMVVdjeNAd8Z8ukLJiIuqrtTnZshRUB6X2M5/JIQ7h2zbM+Exc7Xetr8QSX h1X/LVdMVmwjbB+65HLFxgCQw2nKfF+Bh0T7ovmbfp6jDxnRPB6Srz/GCNB6InkssIi4 j7tJ+P9iMgRCYpPzaz4Y9dPKzC+vTW9c+Fh1F+L8Gl456NxFY6ML56wCl3LsoWEByPum i3+6Nkt94+9UWFvtWzrJjNPL4xPQI69HHISuVIP6h+aCtUyRF21zjiYZtJVkE3x2gXTH Rr/ZgJHdSUwHywB483eDsYqDjsuT0MCp4gCVbiKUwaixoxNYaVwz//jYYQGttrlIPBQ9 +egA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787646866; x=1788251666; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=IVGtX9QFUX57YpBuir6YXJ5ojxTug80HJTjtVuCANHI=; b=izibaPS7/mq/dMUygwFfCjLQSUXIVmWE1lq/LWGGGLKOy3ngJvtpP8caG/CsjbhK/t 2R9w8BBtkZsFm38FaRcPscH+mcQO4oliQhXVd4qX69a/Zj+4V2XOhKAJMIjrmuVl0pMz ONCz+I5uEMeMmv3ENLFwif0nImBIy9Ge9ru69UqExuT8/FCgLusZKEbDhTDDM0x85Yo8 PUe0gvmIm6aLy0Jv3I6m8k1VeJ+aOY1nxN+eBgdT2gJJ0Lx9ljwZ9cAOuE+MTfKdUZPe ICUA+erPEwkE9ZH4c88LzAi2QSxf2SowIgCUq0rz0Sa9PSJd/fw1GMWpYwAUCbIhLKaA Ob7A== X-Forwarded-Encrypted: i=1; AHgh+RriXZ3pQtEIrd0SxUPDmzeUpnANoBITm2q1Tg627X9WrnPaExPfP9JuEBMCSYsCKf8qedf0UPnbPgtoYg81MUHXUkE=@vger.kernel.org X-Gm-Message-State: AFuF++k/cf7t6ym5mP3gWr1hH7obSnGpHwe1K2LwzZvQB9JoeJAJXLGe VjIQ2+DCqPlLL5g/Zo7fW3v7eev43feFHT6lTJXwLxoB6fNg6Sqo1khgi8Ko1NP5Bw== X-Gm-Gg: AR+sD10h+18iErLQeY/iFckpamvC9nPvnLdcxfzR816P8+zmDPCAT5eHBxPpCEEUsTI U50voMEzUAgvk1eVXGOm0LDRmyPReKp+Hknx0hNxLeKl4Qsmg843N48pzveWeU5bU8kmB56rNxy iSCjRuNx3lglbl8Kp74GqDFtcc3YwRTb9otlxc4hubbLtVH8ks8pqMPyyRSDnjbIKvATB53lSiN rxcCtfCQT5dRVmND+TKL8bA7PqyOB0REqP6Hhl3AbgW0QJBr/LWh7dPw21ivep0CKb5Thrku5cR ktc4CwwiQ+xdII8VW3R4R7iY6OJRTH/mOMZc1KWlCoP6lJvUYqNI78e/p8gjn+/xWYL472k8oFl mwC5RR2oOtN2Gip9SVxkfOk3FcFoK2dXQW3KhfM3XVtQaLs9o7sH2JzSHwEX1+JXQdAMy+Z2rxH xbVieZKq/mFCt+ZwRJpNrUhKmxGpiDonN2wlf7ZZK+7+tuxacv+TCR9/wvRZXKLr10wL5er1e7E 1FZe69IGvSIGIxu2ZfQyD+Z9DIAh8eAlLTJlYQMM2c= X-Received: by 2002:a05:6000:2c12:b0:482:bb55:8bdc with SMTP id ffacd0b85a97d-482c0b55514mr40947617f8f.1.1787646865301; Tue, 25 Aug 2026 01:34:25 -0700 (PDT) Received: from google.com (135.91.155.104.bc.googleusercontent.com. [104.155.91.135]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482c9c0acaesm10806759f8f.29.2026.08.25.01.34.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 01:34:24 -0700 (PDT) Date: Tue, 25 Aug 2026 09:34:21 +0100 From: Vincent Donnefort To: ivanimmanuel1234@gmail.com Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] tracing: Fix retry exhaustion in simple ring buffer reader swap Message-ID: References: <20260825-kernel-patch-1-v1-0-e9349aa0b165@gmail.com> <20260825-kernel-patch-1-v1-1-e9349aa0b165@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-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: <20260825-kernel-patch-1-v1-1-e9349aa0b165@gmail.com> On Tue, Aug 25, 2026 at 01:20:37AM -0400, Ivan Immanuel Shaji via B4 Relay wrote: > 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 > Signed-off-by: Ivan Immanuel Shaji Reviewed-by: Vincent Donnefort > --- > 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_buffer.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_rb_per_cpu *cpu_buffer) > overrun = cpu_buffer->meta->overrun; > } while (!simple_bpage_unset_head_link(last, reader, SIMPLE_RB_LINK_NORMAL) && retry--); > > - if (!retry) > - return -EINVAL; > + if (retry < 0) > + return -EBUSY; > > cpu_buffer->head_page = simple_bpage_from_link(reader->link.next); > cpu_buffer->head_page->link.prev = &reader->link; > > -- > 2.53.0 > >