From mboxrd@z Thu Jan 1 00:00:00 1970 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 40F1B2AF13 for ; Mon, 11 Dec 2023 11:40:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Hp/BPQfy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BFBA2C433C8; Mon, 11 Dec 2023 11:40:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1702294839; bh=3gaOmYRIZfbiVmht0OPzyhJS1d5RxKW/OEhIAR90v1o=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Hp/BPQfyYMdM+/l1B7ToTZogugssKh2805pDfssVpBiMrpztnBm3IxhG0xX6GS4Ne 3rnDUW6FCt13YNi6nHSWM2gqNtWEvmdB7+gU2OSZSHRXJKGwMCdCITXV5Cx4iyUfsM MExdTDBqrNSzDjXhrF02RprgNGtivSRedj3mcsSI7ADcY8MbOZ2MxGUITILnohRvGr ne9T+4+mP4tf8dtfJuBUmA0uq/RD2UQLZb29CYbBEMfix86hBRSQugXpkK9WJ/JqHJ aKGRIgmco9nGhO71B8s0XHI1xIcIB/xSORD9NBAqGB37NTR4Y3kX6CacxY54nSiQpH iFYgqWEmxsihQ== Date: Mon, 11 Dec 2023 20:40:33 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Kent Overstreet Subject: Re: [PATCH] ring-buffer: Fix buffer max_data_size with max_event_size Message-Id: <20231211204033.a3658f5f497f0c7541dee025@kernel.org> In-Reply-To: <20231209170925.71d4e02e@gandalf.local.home> References: <20231209170139.33c1b452@gandalf.local.home> <20231209170925.71d4e02e@gandalf.local.home> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit On Sat, 9 Dec 2023 17:09:25 -0500 Steven Rostedt wrote: > On Sat, 9 Dec 2023 17:01:39 -0500 > Steven Rostedt wrote: > > > From: "Steven Rostedt (Google)" > > > > The maximum ring buffer data size is the maximum size of data that can be > > recorded on the ring buffer. Events must be smaller than the sub buffer > > data size minus any meta data. This size is checked before trying to > > allocate from the ring buffer because the allocation assumes that the size > > will fit on the sub buffer. > > > > The maximum size was calculated as the size of a sub buffer page (which is > > currently PAGE_SIZE minus the sub buffer header) minus the size of the > > meta data of an individual event. But it missed the possible adding of a > > time stamp for events that are added long enough apart that the event meta > > data can't hold the time delta. > > > > When an event is added that is greater than the current BUF_MAX_DATA_SIZE > > minus the size of a time stamp, but still less than or equal to > > BUF_MAX_DATA_SIZE, the ring buffer would go into an infinite loop, looking > > for a page that can hold the event. Luckily, there's a check for this loop > > and after 1000 iterations and a warning is emitted and the ring buffer is > > disabled. But this should never happen. > > > > This can happen when a large event is added first, or after a long period > > where an absolute timestamp is prefixed to the event, increasing its size > > by 8 bytes. This passes the check and then goes into the algorithm that > > causes the infinite loop. > > > > Fix this by creating a BUF_MAX_EVENT_SIZE to be used to determine if the > > passed in event is too big for the buffer. > > > > Forgot to add: > > Cc: stable@vger.kernel.org > Fixes: a4543a2fa9ef3 ("ring-buffer: Get timestamp after event is allocated") Looks good to me. Reviewed-by: Masami Hiramatsu (Google) Thanks, > > -- Steve > > > > Reported-by: Kent Overstreet # (on IRC) > > Signed-off-by: Steven Rostedt (Google) > > --- > > 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 8d2a4f00eca9..a38e5a3c6803 100644 > > --- a/kernel/trace/ring_buffer.c > > +++ b/kernel/trace/ring_buffer.c > > @@ -378,6 +378,9 @@ static inline bool test_time_stamp(u64 delta) > > /* Max payload is BUF_PAGE_SIZE - header (8bytes) */ > > #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2)) > > > > +/* Events may have a time stamp attached to them */ > > +#define BUF_MAX_EVENT_SIZE (BUF_MAX_DATA_SIZE - RB_LEN_TIME_EXTEND) > > + > > int ring_buffer_print_page_header(struct trace_seq *s) > > { > > struct buffer_data_page field; > > @@ -3810,7 +3813,7 @@ ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length) > > if (unlikely(atomic_read(&cpu_buffer->record_disabled))) > > goto out; > > > > - if (unlikely(length > BUF_MAX_DATA_SIZE)) > > + if (unlikely(length > BUF_MAX_EVENT_SIZE)) > > goto out; > > > > if (unlikely(trace_recursive_lock(cpu_buffer))) > > @@ -3960,7 +3963,7 @@ int ring_buffer_write(struct trace_buffer *buffer, > > if (atomic_read(&cpu_buffer->record_disabled)) > > goto out; > > > > - if (length > BUF_MAX_DATA_SIZE) > > + if (length > BUF_MAX_EVENT_SIZE) > > goto out; > > > > if (unlikely(trace_recursive_lock(cpu_buffer))) > -- Masami Hiramatsu (Google)