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From: Adam Borowski <kilobyte@angband.pl>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: hang in dax_pmem_compat_release on changing namespace mode
Date: Thu, 19 Sep 2019 17:47:08 +0200
Message-ID: <20190919154708.GA24650@angband.pl> (raw)
In-Reply-To: <CAPcyv4jYE_vmEqe+m7spaXV4FDgHLJpE9cp3Ry2e8vU0JZEFCA@mail.gmail.com>

On Thu, Sep 19, 2019 at 08:10:47AM -0700, Dan Williams wrote:
> On Thu, Sep 19, 2019 at 4:56 AM Adam Borowski <kilobyte@angband.pl> wrote:
> > Hi!
> > If I try to change the mode of a devdax namespace that's in use (mapped by
> > some process), ndctl hangs:
> 
> Is it merely mapped, or might the pages be actively pinned / in use by
> another part of the kernel? The kernel has no choice but to wait for
> active page pins to drain. Can you get a stack trace of the process
> with the dev-dax instance mapped?

Looks like the behaviour is different depending on what the other process
is:
* with qemu, the hang is 100% reproducible, the guest continues to work and
  cleanly exits -- qemu does not exit on its own (unlike normal case) but
  SIGTERM terminates it correctly.  Thus, qemu is not stuck, only ndctl is.
* with mere mmap() (I've used vmemcache) ndctl allows
  reconfiguring the namespace.  No hang.

My way to start qemu is:
.----
#!/bin/sh
NET="-net bridge -net nic"
DISK=eoan-devdax.disk

exec qemu-system-x86_64 -enable-kvm -m 4096,slots=2,maxmem=16G -smp 8 $NET \
 -drive if=none,id=hd,file="$DISK",format=raw,cache=unsafe,discard=on \
 -device virtio-scsi-pci,id=scsi -device scsi-hd,drive=hd \
 -M pc,nvdimm,nvdimm-persistence=mem-ctrl \
 -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax0.0,size=4225761280,align=2M,pmem=on \
 -device nvdimm,id=nvdimm1,memdev=mem1,label-size=256K \
 -vnc :5
`----


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-- 
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⣾⠁⢠⠒⠀⣿⡁ 1kg raspberries, 0.4kg sugar; put into a big jar for 1 month.
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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-19 11:55 Adam Borowski
2019-09-19 15:10 ` Dan Williams
2019-09-19 15:47   ` Adam Borowski [this message]
2019-09-19 15:50     ` Dan Williams
2019-09-19 15:50     ` Adam Borowski

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