On Sat, Sep 08 2012 at 12:50pm -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 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?

I think it much more likely that multipathd will restore a path then an
entirely new table be loaded.

> BTW. there is also -EAGAIN dm_blk_ioctl if dm_suspended_md ... should this
> -EAGAIN be removed too or not?

Don't think it needs to be removed. Here is a patch that addresses the
issue for me.

---

From: Mike Snitzer <snitzer@redhat.com>
Subject: [PATCH] dm mpath: only retry ioctl if queue_if_no_path was configured

commit 35991652b ("dm mpath: allow ioctls to trigger pg init") should
have checked if queue_if_no_path was configured before queueing IO.

Checking for the queue_if_no_path feature, like is done in map_io(),
allows the following table load to work without blocking in the
multipath_ioctl retry loop:

echo "0 1024 multipath 0 0 0 0" | dmsetup create mpath_nodevs

Without this fix the multipath_ioctl will block with the following stack
trace:

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

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
drivers/md/dm-mpath.c | 11 +++++++----
1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index d8abb90..034233e 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1555,6 +1555,7 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd,
unsigned long arg)
{
struct multipath *m = ti->private;
+ struct pgpath *pgpath;
struct block_device *bdev;
fmode_t mode;
unsigned long flags;
@@ -1570,12 +1571,14 @@ again:
if (!m->current_pgpath)
__choose_pgpath(m, 0);

- if (m->current_pgpath) {
- bdev = m->current_pgpath->path.dev->bdev;
- mode = m->current_pgpath->path.dev->mode;
+ pgpath = m->current_pgpath;
+
+ if (pgpath) {
+ bdev = pgpath->path.dev->bdev;
+ mode = pgpath->path.dev->mode;
}

- if (m->queue_io)
+ if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path))
r = -EAGAIN;
else if (!bdev)
r = -EIO;
--
1.7.1

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