Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
On Wed, 12 Sep 2012, Mike Snitzer wrote:
> On Sat, Sep 08 2012 at 12:50pm -0400,
> Mikulas Patocka <mpatocka@xxxxxxxxxx> 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@xxxxxxxxxx>
> 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@xxxxxxxxxx>
> ---
> 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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