On Tue, 4 Sep 2012, Mike Snitzer wrote: > On Tue, Sep 04 2012 at 12:10pm -0400, > Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > On Tue, Sep 04 2012 at 10:58am -0400, > > Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > > > > > On Fri, Aug 31 2012 at 11:04am -0400, > > > David Jeffery <djeffery@xxxxxxxxxx> wrote: > > > > > > > > > > > The DM module recalculates queue limits based only on devices which currently > > > > exist in the table. This creates a problem in the event all devices are > > > > temporarily removed such as all fibre channel paths being lost in multipath. > > > > DM will reset the limits to the maximum permissible, which can then assemble > > > > requests which exceed the limits of the paths when the paths are restored. The > > > > request will fail the blk_rq_check_limits() test when sent to a path with > > > > lower limits, and will be retried without end by multipath. > > > > > > > > This becomes a much bigger issue after fe86cdcef73ba19a2246a124f0ddbd19b14fb549. > > > > Previously, most storage had max_sector limits which exceeded the default > > > > value used. This meant most setups wouldn't trigger this issue as the default > > > > values used when there were no paths were still less than the limits of the > > > > underlying devices. Now that the default stacking values are no longer > > > > constrained, any hardware setup can potentially hit this issue. > > > > > > > > This proposed patch alters the DM limit behavior. With the patch, DM queue > > > > limits only go one way: more restrictive. As paths are removed, the queue's > > > > limits will maintain their current settings. As paths are added, the queue's > > > > limits may become more restrictive. > > > > > > With your proposed patch you could still hit the problem if the > > > initial multipath table load were to occur when no paths exist, e.g.: > > > echo "0 1024 multipath 0 0 0 0" | dmsetup create mpath_nodevs > > > > > > (granted, this shouldn't ever happen.. as is evidenced by the fact > > > that doing so will trigger an existing mpath bug; commit a490a07a67b > > > "dm mpath: allow table load with no priority groups" clearly wasn't > > > tested with the initial table load having no priority groups) > > > > Hi Mikulas, > > > > It seems your new retry in multipath_ioctl (commit 3599165) is causing > > problems for the above dmsetup create. > > > > Here is the stack trace for a hang that resulted as a side-effect of > > udev starting blkid for the newly created multipath device: > > > > blkid D 0000000000000002 0 23936 1 0x00000000 > > ffff8802b89e5cd8 0000000000000082 ffff8802b89e5fd8 0000000000012440 > > ffff8802b89e4010 0000000000012440 0000000000012440 0000000000012440 > > ffff8802b89e5fd8 0000000000012440 ffff88030c2aab30 ffff880325794040 > > Call Trace: > > [<ffffffff814ce099>] schedule+0x29/0x70 > > [<ffffffff814cc312>] schedule_timeout+0x182/0x2e0 > > [<ffffffff8104dee0>] ? lock_timer_base+0x70/0x70 > > [<ffffffff814cc48e>] schedule_timeout_uninterruptible+0x1e/0x20 > > [<ffffffff8104f840>] msleep+0x20/0x30 > > [<ffffffffa0000839>] multipath_ioctl+0x109/0x170 [dm_multipath] > > [<ffffffffa06bfb9c>] dm_blk_ioctl+0xbc/0xd0 [dm_mod] > > [<ffffffff8122a408>] __blkdev_driver_ioctl+0x28/0x30 > > [<ffffffff8122a79e>] blkdev_ioctl+0xce/0x730 > > [<ffffffff811970ac>] block_ioctl+0x3c/0x40 > > [<ffffffff8117321c>] do_vfs_ioctl+0x8c/0x340 > > [<ffffffff81166293>] ? sys_newfstat+0x33/0x40 > > [<ffffffff81173571>] sys_ioctl+0xa1/0xb0 > > [<ffffffff814d70a9>] system_call_fastpath+0x16/0x1b > > FYI, here is the full blkid command line: > /sbin/blkid -o udev -p /dev/dm-8 It's hard to say what should be done correctly ... if you create a multipath device with "queue_if_no_path" and no active path, it should delay all requests until a path becomes available ... and it is doing that. Maybe we could move the waiting loop up to dm_blk_ioctl so that it unlocks when someone reloads the target? BTW. there is also -EAGAIN dm_blk_ioctl if dm_suspended_md ... should this -EAGAIN be removed too or not? Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
