https://bugzilla.kernel.org/show_bug.cgi?id=118281 Bug ID: 118281 Summary: SCSI disk driver (sd) bug (wrong max_sectors value) Product: SCSI Drivers Version: 2.5 Kernel Version: 4.6 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: Other Assignee: scsi_drivers-other@xxxxxxxxxxxxxxxxxxxx Reporter: alexin.ivan@xxxxxxxxx Regression: No Problem: incorrect 'max_sectors_kb' value calculaton after commit (https://github.com/torvalds/linux/commit/d0eb20a863ba7dc1d3f4b841639671f134560be2). Examining this code(https://github.com/torvalds/linux/blob/v4.6/drivers/scsi/sd.c#L2850): ``` //... /* Initial block count limit based on CDB TRANSFER LENGTH field size. */ dev_max = sdp->use_16_for_rw ? SD_MAX_XFER_BLOCKS : SD_DEF_XFER_BLOCKS; /* Some devices report a maximum block count for READ/WRITE requests. */ dev_max = min_not_zero(dev_max, sdkp->max_xfer_blocks); q->limits.max_dev_sectors = logical_to_sectors(sdp, dev_max); /* * Use the device's preferred I/O size for reads and writes * unless the reported value is unreasonably small, large, or * garbage. */ if (sdkp->opt_xfer_blocks && sdkp->opt_xfer_blocks <= dev_max && sdkp->opt_xfer_blocks <= SD_DEF_XFER_BLOCKS && sdkp->opt_xfer_blocks * sdp->sector_size >= PAGE_SIZE) //NOTE!: Assigning new 'rw_max' value in bytes here rw_max = q->limits.io_opt = sdkp->opt_xfer_blocks * sdp->sector_size; else rw_max = BLK_DEF_MAX_SECTORS; /* Combine with controller limits */ //NOTE!: Comparing bytes to sectors here (rw_max:bytes, max_hw_sectros:sectors). q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q)); ``` We can see that comparing 'rw_max' value (measured in bytes) to 'queue_max_hw_sectors(q)' (measured in sectors) causing error: 'max_sectors' value becomes equal to 'queue_max_hw_sectors(q)' value. For example (assuming sector_size = 512): Let sdkp->opt_xfer_blocks == 10160. 10160 * 512 == (rw_max = q->limits.io_opt = sdkp->opt_xfer_blocks * sdp->sector_size) Let also max_hw_sectors == 0xFFFF, so, (keeping in mind 0xFFFF < 10160 * 512) 'max_sectors' value will be set to minimal value (0xFFFF). Another example: ``` root@srv28:~# uname -a Linux srv28 4.4.0-22-generic #39-Ubuntu SMP Thu May 5 16:53:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux root@srv28:~# sg_vpd --page=0xb0 /dev/sdd | grep "Maximum transfer length" Maximum transfer length: 10160 blocks root@srv28:~# cat /sys/block/dm-0/slaves/*/queue/max_hw_sectors_kb 32767 32767 ``` ``` root@srv32:~# uname -a Linux srv32 3.19.0-59-generic #65~14.04.1-Ubuntu SMP Tue Apr 19 18:57:09 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux root@srv32:~# sg_vpd --page=0xb0 /dev/sdb | grep "Maximum transfer length" Maximum transfer length: 10160 blocks root@srv32:~# cat /sys/block/dm-*/slaves/*/queue/max_sectors_kb 5080 5080 5080 ``` Possible bugfix (assigning correct value to 'rw_max'): ``` //... rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks); q->limits.io_opt = sdkp->opt_xfer_blocks * sdp->sector_size; //... ``` Readable description: https://gist.github.com/alexin-ivan/d23ba61dac7ae2b31acf75facad86680 -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
