On Thu, Mar 18, 2021 at 01:53:40PM +0100, Christoph Hellwig wrote: > On Thu, Mar 18, 2021 at 11:29:50AM +0000, Matthew Wilcox wrote: > > On Thu, Mar 18, 2021 at 07:39:22AM +0100, Christoph Hellwig wrote: > > > @@ -536,7 +518,7 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b, > > > b->max_write_zeroes_sectors); > > > t->max_zone_append_sectors = min(t->max_zone_append_sectors, > > > b->max_zone_append_sectors); > > > - t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn); > > > + t->bounce = min_not_zero(t->bounce, b->bounce); > > > > I see how min_not_zero() made sense when it was a pfn. Does it still > > make sense now it's an enum? I would have thought it'd now be 'max()', > > given the definitions later on. > > Actually, blk_stack_limits should not look at ->bounce_pfn / ->bounce > at all. blk_queue_bounce is only called my blk_mq_submit_bio, and > the only stacked blk-mq driver (dm-mpath) does not need bouncing. > > I'll add a patch to fix this up to the front of the series. Is blk_queue_bounce() called again when mpath submits the request to the lower device? I thought when I looked at this code some time ago bouncing would only be checked the first time a request is created (dm-mpath), and then not again, so when we don't check for whether bouncing is necessary in mpath, we still might screw the LLD - hence why we might inherit this via the limits. -- Best Regards, Benjamin Block / Linux on IBM Z Kernel Development / IBM Systems IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy Vorsitz. AufsR.: Gregor Pillen / Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: AmtsG Stuttgart, HRB 243294
