[dm-devel] block: disallow changing max_sectors_kb on a request stacking device
Mike Snitzer
snitzer at redhat.com
Mon Nov 7 16:40:30 UTC 2016
On Fri, Oct 28 2016 at 3:45pm -0400,
Mike Snitzer <snitzer at redhat.com> wrote:
> Otherwise users can easily shoot themselves in the foot by creating the
> situation where the top-level stacked device (e.g. DM multipath) has a
> larger max_sectors_kb than the underlying device(s). Which will
> certainly lead to IO errors due to the "over max size limit" check in
> blk_cloned_rq_check_limits().
>
> Use of WARN_ON_ONCE() gives users visibility into which application
> attempted to perform this unsupported max_sectors_kb change.
>
> This is a crude, yet effective, solution that forces the use of system
> software (e.g. udev rules or multipathd) to tweak max_sectors_kb of the
> underlying devices _before_ a layer like DM multipath is layered ontop.
>
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
> ---
> block/blk-sysfs.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
> index 9cc8d7c..cce43d7 100644
> --- a/block/blk-sysfs.c
> +++ b/block/blk-sysfs.c
> @@ -199,8 +199,12 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
> unsigned long max_sectors_kb,
> max_hw_sectors_kb = queue_max_hw_sectors(q) >> 1,
> page_kb = 1 << (PAGE_SHIFT - 10);
> - ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
> + ssize_t ret;
> +
> + if (WARN_ON_ONCE(blk_queue_stackable(q)))
> + return -EINVAL;
>
> + ret = queue_var_store(&max_sectors_kb, page, count);
> if (ret < 0)
> return ret;
>
> --
> 2.8.4 (Apple Git-73)
Jens,
Never heard from you on this patch. Would you like me to resend without
the WARN_ON_ONCE? (Failing is enough, the userspace code that attempts
to set max_sectors_kb on DM multipath will get the user's attention)
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