On Wed, May 22, 2024 at 04:24:58PM +0200, Christoph Hellwig wrote: > On Tue, May 21, 2024 at 10:51:17PM -0400, Mike Snitzer wrote: > > Otherwise, blk_validate_limits() will throw-away the max_sectors that > > was stacked from underlying device(s). In doing so it can set a > > max_sectors limit that violates underlying device limits. > > Hmm, yes it sort of is "throwing the limit away", but it really > recalculates it from max_hw_sectors, max_dev_sectors and user_max_sectors. Yes, but it needs to do that recalculation at each level of a stacked device. And then we need to combine them via blk_stack_limits() -- as is done with the various limits stacking loops in drivers/md/dm-table.c:dm_calculate_queue_limits > > This caused dm-multipath IO failures like the following because the > > underlying devices' max_sectors were stacked up to be 1024, yet > > blk_validate_limits() defaulted max_sectors to BLK_DEF_MAX_SECTORS_CAP > > (2560): > > I suspect the problem is that SCSI messed directly with max_sectors instead > and ignores max_user_sectors (and really shouldn't touch either, but that's > a separate discussion). Can you try the patch below and maybe also provide > the sysfs output for max_sectors_kb and max_hw_sectors_kb for all involved > devices? FYI, you can easily reproduce with: git clone https://github.com/snitm/mptest.git cd mptest <edit so it uses: export MULTIPATH_BACKEND_MODULE="scsidebug"> ./runtest ./tests/test_00_no_failure Also, best to change this line: ./lib/mpath_generic: local _feature="4 queue_if_no_path retain_attached_hw_handler queue_mode $MULTIPATH_QUEUE_MODE" to: ./lib/mpath_generic: local _feature="3 retain_attached_hw_handler queue_mode $MULTIPATH_QUEUE_MODE" Otherwise the test will hang due to queue_if_no_path. all underlying scsi-debug scsi devices: ./max_hw_sectors_kb:2147483647 ./max_sectors_kb:512 multipath device: before my fix: ./max_hw_sectors_kb:2147483647 ./max_sectors_kb:1280 after my fix: ./max_hw_sectors_kb:2147483647 ./max_sectors_kb:512 > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c > index 332eb9dac22d91..f6c822c9cbd2d3 100644 > --- a/drivers/scsi/sd.c > +++ b/drivers/scsi/sd.c > @@ -3700,8 +3700,10 @@ static int sd_revalidate_disk(struct gendisk *disk) > */ > if (sdkp->first_scan || > q->limits.max_sectors > q->limits.max_dev_sectors || > - q->limits.max_sectors > q->limits.max_hw_sectors) > + q->limits.max_sectors > q->limits.max_hw_sectors) { > q->limits.max_sectors = rw_max; > + q->limits.max_user_sectors = rw_max; > + } > > sdkp->first_scan = 0; > > Driver shouldn't be changing max_user_sectors.. But it also didn't fix it (mpath still gets ./max_sectors_kb:1280): [ 74.872485] blk_insert_cloned_request: over max size limit. (2048 > 1024) [ 74.872505] device-mapper: multipath: 254:3: Failing path 8:16. [ 74.872620] blk_insert_cloned_request: over max size limit. (2048 > 1024) [ 74.872641] device-mapper: multipath: 254:3: Failing path 8:32. [ 74.872712] blk_insert_cloned_request: over max size limit. (2048 > 1024) [ 74.872732] device-mapper: multipath: 254:3: Failing path 8:48. [ 74.872788] blk_insert_cloned_request: over max size limit. (2048 > 1024) [ 74.872808] device-mapper: multipath: 254:3: Failing path 8:64. Simply setting max_user_sectors won't help with stacked devices because blk_stack_limits() doesn't stack max_user_sectors. It'll inform the underlying device's blk_validate_limits() calculation which will result in max_sectors having the desired value (which it already did, as I showed above). But when stacking limits from underlying devices up to the higher-level dm-mpath queue_limits we still have information loss. Mike
