On Mon, Feb 06, 2023 at 04:02:46PM -0800, Bart Van Assche wrote:
> On 2/1/23 15:50, Luis Chamberlain wrote:
> > On Mon, Jan 30, 2023 at 01:26:51PM -0800, Bart Van Assche wrote:
> > > @@ -122,12 +177,17 @@ EXPORT_SYMBOL(blk_queue_bounce_limit);
> > > void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
> > > {
> > > struct queue_limits *limits = &q->limits;
> > > + unsigned int min_max_hw_sectors = PAGE_SIZE >> SECTOR_SHIFT;
> > > unsigned int max_sectors;
> > > - if ((max_hw_sectors << 9) < PAGE_SIZE) {
> > > - max_hw_sectors = 1 << (PAGE_SHIFT - 9);
> > > - printk(KERN_INFO "%s: set to minimum %d\n",
> > > - __func__, max_hw_sectors);
> > > + if (max_hw_sectors < min_max_hw_sectors) {
> > > + blk_enable_sub_page_limits(limits);
> > > + min_max_hw_sectors = 1;
> > > + }
> >
> > Up to this part this a non-functional update, and so why not a
> > separate patch to clarify that.
>
> Will do.
>
> > > +
> > > + if (max_hw_sectors < min_max_hw_sectors) {
> > > + max_hw_sectors = min_max_hw_sectors;
> > > + pr_info("%s: set to minimum %u\n", __func__, max_hw_sectors);
> >
> > But if I understand correctly here we're now changing
> > max_hw_sectors from 1 to whatever the driver set on
> > blk_queue_max_hw_sectors() if its smaller than PAGE_SIZE.
> >
> > To determine if this is a functional change it begs the
> > question as to how many block drivers have a max hw sector
> > smaller than the equivalent PAGE_SIZE and wonder if that
> > could regress.
>
> If a block driver passes an argument to blk_queue_max_hw_sectors() or
> blk_queue_max_segment_size() that is smaller than what is supported by the
> block layer, data corruption will be triggered if the block driver or the
> hardware supported by the block driver does not support the larger values
> chosen by the block layer. Changing limits that will trigger data corruption
> into limits that may work seems like an improvement to me?
Wow, clearly! Without a doubt!
But I'm trying to do a careful review here.
The commit log did not describe what *does* happen in these situations today,
and you seem to now be suggesting in the worst case corruption can happen.
That changes the patch context quite a bit!
My question above still stands though, how many block drivers have a max
hw sector smaller than the equivalent PAGE_SIZE. If you make your
change, even if it fixes some new use case where corruption is seen, can
it regress some old use cases for some old controllers?
Luis
