hang in dax_pmem_compat_release on changing namespace mode

From: Adam Borowski <kilobyte@angband.pl>
To: linux-nvdimm@lists.01.org, Dan Williams <dan.j.williams@intel.com>
Subject: hang in dax_pmem_compat_release on changing namespace mode
Date: Thu, 19 Sep 2019 13:55:47 +0200	[thread overview]
Message-ID: <20190919115547.GA17963@angband.pl> (raw)

Hi!
If I try to change the mode of a devdax namespace that's in use (mapped by
some process), ndctl hangs:

[ 9546.754673] INFO: task ndctl:3907 blocked for more than 1208 seconds.
[ 9546.754677]       Not tainted 5.3.0-00048-g7f09b8bce091 #1
[ 9546.754679] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 9546.754681] ndctl           D    0  3907   3856 0x00004004
[ 9546.754684] Call Trace:
[ 9546.754689]  ? __schedule+0x281/0x670
[ 9546.754692]  ? __switch_to_asm+0x34/0x70
[ 9546.754694]  ? __switch_to_asm+0x34/0x70
[ 9546.754696]  schedule+0x39/0xa0
[ 9546.754699]  schedule_timeout+0x22b/0x320
[ 9546.754701]  ? __switch_to_asm+0x34/0x70
[ 9546.754703]  ? __switch_to_asm+0x40/0x70
[ 9546.754705]  ? __switch_to_asm+0x34/0x70
[ 9546.754707]  ? __switch_to+0x162/0x440
[ 9546.754710]  ? apic_timer_interrupt+0xa/0x20
[ 9546.754712]  wait_for_completion+0x100/0x150
[ 9546.754714]  ? wake_up_q+0x60/0x60
[ 9546.754718]  dev_pagemap_cleanup+0x47/0x60
[ 9546.754720]  devm_memremap_pages_release+0xc5/0x220
[ 9546.754724]  release_nodes+0x221/0x270
[ 9546.754728]  dax_pmem_compat_release+0x30/0x50 [dax_pmem_compat]
[ 9546.754730]  ? dax_pmem_compat_remove+0x20/0x20 [dax_pmem_compat]
[ 9546.754733]  device_for_each_child+0x57/0x90
[ 9546.754736]  dax_pmem_compat_remove+0x13/0x20 [dax_pmem_compat]
[ 9546.754739]  nvdimm_bus_remove+0x4e/0xc0
[ 9546.754741]  device_release_driver_internal+0xd8/0x1b0
[ 9546.754743]  unbind_store+0xff/0x130
[ 9546.754746]  kernfs_fop_write+0x140/0x1b0
[ 9546.754749]  vfs_write+0xe4/0x1d0
[ 9546.754751]  ksys_write+0x70/0x100
[ 9546.754754]  do_syscall_64+0x50/0x100
[ 9546.754756]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 9546.754758] RIP: 0033:0x7f2d375dfad4
[ 9546.754762] Code: Bad RIP value.
[ 9546.754763] RSP: 002b:00007ffd61eca4e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 9546.754766] RAX: ffffffffffffffda RBX: 000055fb48f0982f RCX: 00007f2d375dfad4
[ 9546.754767] RDX: 0000000000000007 RSI: 000055fb48f0982f RDI: 0000000000000003
[ 9546.754769] RBP: 0000000000000007 R08: 00000000ffffffff R09: 00007ffd61eca3c0
[ 9546.754770] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
[ 9546.754771] R13: 00007f2d37166e70 R14: 0000000000000000 R15: 000055fb48f0c900

Fake pmem (memmap=4G!16G), the command is:
    ndctl create-namespace -e namespace0.0 -m fsdax -f
-f is needed as a label-less fake pmem namespace is always active.

According to the man page, reconfiguring in that case is not allowed (duh),
and the operation is supposed to gracefully fail.

Meow!
-- 
⢀⣴⠾⠻⢶⣦⠀ A MAP07 (Dead Simple) raspberry tincture recipe: 0.5l 95% alcohol,
⣾⠁⢠⠒⠀⣿⡁ 1kg raspberries, 0.4kg sugar; put into a big jar for 1 month.
⢿⡄⠘⠷⠚⠋⠀ Filter out and throw away the fruits (can dump them into a cake,
⠈⠳⣄⠀⠀⠀⠀ etc), let the drink age at least 3-6 months.
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