Re: [PATCH 2/2] blktrace: limit allowed total trace buffer size

[Su Yue <l@damenly.su>]

On Tue 23 Mar 2021 at 16:14, Ming Lei <ming.lei@redhat.com> wrote:

> On some ARCHs, such as aarch64, page size may be 64K, meantime 
> there may
> be lots of CPU cores. relay_open() needs to allocate pages on 
> each CPU
> blktrace, so easily too many pages are taken by blktrace. For 
> example,
> on one ARM64 server: 224 CPU cores, 16G RAM, blktrace finally 
> got
> allocated 7GB in case of 'blktrace -b 8192' which is used by 
> device-mapper
> test suite[1]. This way could cause OOM easily.
>
> Fix the issue by limiting max allowed pages to be 1/8 of 
> totalram_pages().
>
> [1] https://github.com/jthornber/device-mapper-test-suite.git
>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  kernel/trace/blktrace.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index c221e4c3f625..8403ff19d533 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -466,6 +466,35 @@ static void blk_trace_setup_lba(struct 
> blk_trace *bt,
>  	}
>  }
>
> +/* limit total allocated buffer size is <= 1/8 of total pages 
> */
> +static void validate_and_adjust_buf(struct blk_user_trace_setup 
> *buts)
> +{
> +	unsigned buf_size = buts->buf_size;
> +	unsigned buf_nr = buts->buf_nr;
> +	unsigned long max_allowed_pages = totalram_pages() >> 3;
> +	unsigned long req_pages = PAGE_ALIGN(buf_size * buf_nr) >> 
> PAGE_SHIFT;
> +
> +	if (req_pages * num_online_cpus() <= max_allowed_pages)
> +		return;
> +
> +	req_pages = DIV_ROUND_UP(max_allowed_pages, 
> num_online_cpus());
> +
> +	if (req_pages == 0) {
> +		buf_size = PAGE_SIZE;
> +		buf_nr = 1;
> +	} else {
> +		buf_size = req_pages << PAGE_SHIFT / buf_nr;
>
Should it be:
buf_size = (req_pages << PAGE_SHIFT) / buf_nr;
?
The priority of '<<' is lower than '/', right? :)

--
Su
> +		if (buf_size < PAGE_SIZE)
> +			buf_size = PAGE_SIZE;
> +		buf_nr = req_pages << PAGE_SHIFT / buf_size;
> +		if (buf_nr == 0)
> +			buf_nr = 1;
> +	}
> +
> +	buts->buf_size = min_t(unsigned, buf_size, buts->buf_size);
> +	buts->buf_nr = min_t(unsigned, buf_nr, buts->buf_nr);
> +}
> +
>  /*
>   * Setup everything required to start tracing
>   */
> @@ -482,6 +511,9 @@ static int do_blk_trace_setup(struct 
> request_queue *q, char *name, dev_t dev,
>  	if (!buts->buf_size || !buts->buf_nr)
>  		return -EINVAL;
>
> +	/* make sure not allocate too much for userspace */
> +	validate_and_adjust_buf(buts);
> +
>  	strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
>  	buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';