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Mauricio Faria de Oliveira authored
commit 47796938 upstream. This reverts commit a1989b33. That commit introduced a regression at least for the case of the SG_IO ioctl() running without CAP_SYS_RAWIO capability (e.g., unprivileged users) when there are no active paths: the ioctl() fails with the ENOTTY errno immediately rather than blocking due to queue_if_no_path until a path becomes active, for example. That case happens to be exercised by QEMU KVM guests with 'scsi-block' devices (qemu "-device scsi-block" [1], libvirt "<disk type='block' device='lun'>" [2]) from multipath devices; which leads to SCSI/filesystem errors in such a guest. More general scenarios can hit that regression too. The following demonstration employs a SG_IO ioctl() with a standard SCSI INQUIRY command for this objective (some output & user changes omitted for brevity and comments added for clarity). Reverting that commit restores normal operation (queueing) in failing scenarios; tested on linux-next (next-20151022). 1) Test-case is based on sg_simple0 [3] (just SG_IO; remove SG_GET_VERSION_NUM) $ cat sg_simple0.c ... see [3] ... $ sed '/SG_GET_VERSION_NUM/,/}/d' sg_simple0.c > sgio_inquiry.c $ gcc sgio_inquiry.c -o sgio_inquiry 2) The ioctl() works fine with active paths present. # multipath -l 85ag56 85ag56 (...) dm-19 IBM ,2145 size=60G features='1 queue_if_no_path' hwhandler='0' wp=rw |-+- policy='service-time 0' prio=0 status=active | |- 8:0:11:0 sdz 65:144 active undef running | `- 9:0:9:0 sdbf 67:144 active undef running `-+- policy='service-time 0' prio=0 status=enabled |- 8:0:12:0 sdae 65:224 active undef running `- 9:0:12:0 sdbo 68:32 active undef running $ ./sgio_inquiry /dev/mapper/85ag56 Some of the INQUIRY command's response: IBM 2145 0000 INQUIRY duration=0 millisecs, resid=0 3) The ioctl() fails with ENOTTY errno with _no_ active paths present, for unprivileged users (rather than blocking due to queue_if_no_path). # for path in $(multipath -l 85ag56 | grep -o 'sd[a-z]\+'); \ do multipathd -k"fail path $path"; done # multipath -l 85ag56 85ag56 (...) dm-19 IBM ,2145 size=60G features='1 queue_if_no_path' hwhandler='0' wp=rw |-+- policy='service-time 0' prio=0 status=enabled | |- 8:0:11:0 sdz 65:144 failed undef running | `- 9:0:9:0 sdbf 67:144 failed undef running `-+- policy='service-time 0' prio=0 status=enabled |- 8:0:12:0 sdae 65:224 failed undef running `- 9:0:12:0 sdbo 68:32 failed undef running $ ./sgio_inquiry /dev/mapper/85ag56 sg_simple0: Inquiry SG_IO ioctl error: Inappropriate ioctl for device 4) dmesg shows that scsi_verify_blk_ioctl() failed for SG_IO (0x2285); it returns -ENOIOCTLCMD, later replaced with -ENOTTY in vfs_ioctl(). $ dmesg <...> [] device-mapper: multipath: Failing path 65:144. [] device-mapper: multipath: Failing path 67:144. [] device-mapper: multipath: Failing path 65:224. [] device-mapper: multipath: Failing path 68:32. [] sgio_inquiry: sending ioctl 2285 to a partition! 5) The ioctl() only works if the SYS_CAP_RAWIO capability is present (then queueing happens -- in this example, queue_if_no_path is set); this is due to a conditional check in scsi_verify_blk_ioctl(). # capsh --drop=cap_sys_rawio -- -c './sgio_inquiry /dev/mapper/85ag56' sg_simple0: Inquiry SG_IO ioctl error: Inappropriate ioctl for device # ./sgio_inquiry /dev/mapper/85ag56 & [1] 72830 # cat /proc/72830/stack [<c00000171c0df700>] 0xc00000171c0df700 [<c000000000015934>] __switch_to+0x204/0x350 [<c000000000152d4c>] msleep+0x5c/0x80 [<c00000000077dfb0>] dm_blk_ioctl+0x70/0x170 [<c000000000487c40>] blkdev_ioctl+0x2b0/0x9b0 [<c0000000003128e4>] block_ioctl+0x64/0xd0 [<c0000000002dd3b0>] do_vfs_ioctl+0x490/0x780 [<c0000000002dd774>] SyS_ioctl+0xd4/0xf0 [<c000000000009358>] system_call+0x38/0xd0 6) This is the function call chain exercised in this analysis: SYSCALL_DEFINE3(ioctl, <...>) @ fs/ioctl.c -> do_vfs_ioctl() -> vfs_ioctl() ... error = filp->f_op->unlocked_ioctl(filp, cmd, arg); ... -> dm_blk_ioctl() @ drivers/md/dm.c -> multipath_ioctl() @ drivers/md/dm-mpath.c ... (bdev = NULL, due to no active paths) ... if (!bdev || <...>) { int err = scsi_verify_blk_ioctl(NULL, cmd); if (err) r = err; } ... -> scsi_verify_blk_ioctl() @ block/scsi_ioctl.c ... if (bd && bd == bd->bd_contains) // not taken (bd = NULL) return 0; ... if (capable(CAP_SYS_RAWIO)) // not taken (unprivileged user) return 0; ... printk_ratelimited(KERN_WARNING "%s: sending ioctl %x to a partition!\n" <...>); return -ENOIOCTLCMD; <- ... return r ? : <...> <- ... if (error == -ENOIOCTLCMD) error = -ENOTTY; out: return error; ... Links: [1] http://git.qemu.org/?p=qemu.git;a=commit;h=336a6915bc7089fb20fea4ba99972ad9a97c5f52 [2] https://libvirt.org/formatdomain.html#elementsDisks (see 'disk' -> 'device') [3] http://tldp.org/HOWTO/SCSI-Generic-HOWTO/pexample.html (Revision 1.2, 2002-05-03) Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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