Re: while (1) in btrfs_relocate_block_group didn't end

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/9/29 上午2:36, Cebtenzzre wrote:
> On Mon, 2019-09-16 at 17:20 -0400, Cebtenzzre wrote:
>> On Sat, 2019-09-14 at 17:36 -0400, Cebtenzzre wrote:
>>> Hi,
>>>
>>> I started a balance of one block group, and I saw this in dmesg:
>>>
>>> BTRFS info (device sdi1): balance: start -dvrange=2236714319872..2236714319873
>>> BTRFS info (device sdi1): relocating block group 2236714319872 flags data|raid0
>>> BTRFS info (device sdi1): found 1 extents
>>> BTRFS info (device sdi1): found 1 extents
>>> BTRFS info (device sdi1): found 1 extents
>>> BTRFS info (device sdi1): found 1 extents
>>> BTRFS info (device sdi1): found 1 extents
>>>
>>> [...]
>>>
>>> I am using Arch Linux with kernel version 5.2.14-arch2, and I specified
>>> "slub_debug=P,kmalloc-2k" in the kernel cmdline to detect and protect
>>> against a use-after-free that I found when I had KASAN enabled. Would
>>> that kernel parameter result in a silent retry if it hit the use-after-
>>> free?
>>
>> Please disregard the quoted message. This behavior does appear to be a
>> result of using the slub_debug option instead of KASAN. It is not
>> directly caused by BTRFS.
> 
> Actually, I just reproduced this behavior without slub_debug in the
> cmdline, on Linux 5.3.0 with "[PATCH] btrfs: relocation: Fix KASAN
> report about use-after-free due to dead reloc tree cleanup race" (
> https://patchwork.kernel.org/patch/11153729/) applied.
> 
> So, this issue is still relevant and possible to trigger, though under
> different conditions (different volume, kernel version, and cmdline).
> 

That patch is not to solve the while loop problem, so we still need some
extra info for this problem.

Is the problem always reproducible on that fs or still with some randomness?

And, can you still reproduce it with v5.1/v5.2?

Thanks,
Qu


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