From 0fd9b8b499b31651d3b2d1c837a0f199ea25cc41 Mon Sep 17 00:00:00 2001 From: Mauricio Faria de Oliveira Date: Thu, 29 Oct 2015 10:24:23 -0200 Subject: [PATCH] Revert "dm mpath: fix stalls when handling invalid ioctls" commit 47796938c46b943d157ac8a6f9ed4e3b98b83cf4 upstream. This reverts commit a1989b330093578ea5470bea0a00f940c444c466. 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 "" [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 [] 0xc00000171c0df700 [] __switch_to+0x204/0x350 [] msleep+0x5c/0x80 [] dm_blk_ioctl+0x70/0x170 [] blkdev_ioctl+0x2b0/0x9b0 [] block_ioctl+0x64/0xd0 [] do_vfs_ioctl+0x490/0x780 [] SyS_ioctl+0xd4/0xf0 [] 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 Signed-off-by: Mike Snitzer Signed-off-by: Greg Kroah-Hartman --- drivers/md/dm-mpath.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-) diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c index 0ba21b0f3972..eb7ddb20fd48 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -1608,11 +1608,8 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd, /* * Only pass ioctls through if the device sizes match exactly. */ - if (!bdev || ti->len != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT) { - int err = scsi_verify_blk_ioctl(NULL, cmd); - if (err) - r = err; - } + if (!r && ti->len != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT) + r = scsi_verify_blk_ioctl(NULL, cmd); if (r == -ENOTCONN && !fatal_signal_pending(current)) queue_work(kmultipathd, &m->process_queued_ios); -- 2.20.1