On Thu, May 23, 2024 at 04:49:38PM +0200, Christoph Hellwig wrote: > On Thu, May 23, 2024 at 10:12:24AM -0400, Mike Snitzer wrote: > > Not sure what is sketchy about the max_sectors == 0 check, the large > > comment block explains that check quite well. We want to avoid EIO > > for unsupported operations (otherwise we'll get spurious path failures > > in the context of dm-multipath). Could be we can remove this check > > after an audit of how LLD handle servicing IO for unsupported > > operations -- so best to work through it during a devel cycle. > > Think of what happens if you create a dm device, and then reduce > max_sectors using sysfs on the lower device after the dm device > was created: you'll trivially trigger this check. > > > Not sure why scsi_debug based testing with mptest isn't triggering it > > for you. Are you seeing these limits for the underlying scsi_debug > > devices? > > > > ./max_hw_sectors_kb:2147483647 > > ./max_sectors_kb:512 > > root@testvm:~/mptest# cat /sys/block/sdc/queue/max_hw_sectors_kb > 2147483647 > > root@testvm:~/mptest# cat /sys/block/sdd/queue/max_sectors_kb > 512 > > root@testvm:~/mptest# cat /sys/block/dm-0/queue/max_hw_sectors_kb > 2147483647 > > root@testvm:~/mptest# cat /sys/block/dm-0/queue/max_sectors_kb > 1280 > > so they don't match, but for some reason bigger bios never get built. Weird... I'm running in a VMware guest but I don't see why that'd make a difference on larger IOs being formed (given it is virtual scsi_debug devices). In any case, we know I can reproduce with this scsi_debug-based mptest test and Marco has verified my fix resolves the issue on his FC multipath testbed. But I've just floated a patch to elevate the fix to block core (based on Ming's suggestion): https://patchwork.kernel.org/project/dm-devel/patch/Zk9i7V2GRoHxBPRu@xxxxxxxxxx/ Let me know, thanks.
