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Re: [Qemu-block] [PATCH 0/1] block: Workaround for the iotests errors
From: |
Jeff Cody |
Subject: |
Re: [Qemu-block] [PATCH 0/1] block: Workaround for the iotests errors |
Date: |
Fri, 24 Nov 2017 01:12:34 -0500 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
On Fri, Nov 24, 2017 at 01:57:46AM +0800, Fam Zheng wrote:
> Jeff's block job patch made the latent drain bug visible, and I find this
> patch, which by itself also makes some sense, can hide it again. :) With it
> applied we are at least back to the ground where patchew's iotests (make
> address@hidden) can pass.
>
Unfortunately, I am still seeing segfaults and aborts even with this patch.
For instance, on tests: 097 141 176.
k
> The real bug is that in the middle of bdrv_parent_drained_end(), bs's parent
> list changes. One drained_end call before the mirror_exit() already did one
> blk_root_drained_end(), a second drained_end on an updated parent node can do
> another same blk_root_drained_end(), making it unbalanced with
> blk_root_drained_begin(). This is shown by the following three backtraces as
> captured by rr with a crashed "qemu-img commit", essentially the same as in
> the failed iotest 020:
>
> * Backtrace 1, where drain begins:
>
> (rr) bt
>
> * Backtrace 2, in the early phase of bdrv_parent_drained_end(), before
> mirror_exit happend:
>
> (rr) bt
>
> * Backtrace 3, in a later phase of the same bdrv_parent_drained_end(), after
> mirror_exit() which changed the node graph:
>
> (rr) bt
>
> IMO we should rethink bdrv_parent_drained_begin/end to avoid such
> complications
> and maybe in the long term get rid of the nested BDRV_POLL_WHILE() if
> possible.
>
> It's late for me so I'm posting the patch anyway in case we could use it for
> -rc3.
>
> Note this doesn't fix the hanging 056, which I haven't debugged yet.
>
> Fam
>
> Fam Zheng (1):
> block: Don't poll for drain end
>
> block/io.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> --
> 2.14.3
>