linux-ext4 - Re: dax pmd fault handler never returns to userspace

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Date:	Wed, 18 Nov 2015 12:43:01 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	Ross Zwisler <ross.zwisler@...el.com>
Subject: Re: dax pmd fault handler never returns to userspace

Ross Zwisler <ross.zwisler@...ux.intel.com> writes:

> On Wed, Nov 18, 2015 at 08:52:59AM -0800, Dan Williams wrote:
>> Sysrq-t or sysrq-w dump?  Also do you have the locking fix from Yigal?
>> 
>> https://lists.01.org/pipermail/linux-nvdimm/2015-November/002842.html
>
> I was able to reproduce the issue in my setup with v4.3, and the patch from
> Yigal seems to solve it.  Jeff, can you confirm?

I applied the patch from Yigal and the symptoms persist.  Ross, what are
you testing on?  I'm using an NVDIMM-N.

Dan, here's sysrq-l (which is what w used to look like, I think).  Only
cpu 3 is interesting:

[  825.339264] NMI backtrace for cpu 3
[  825.356347] CPU: 3 PID: 13555 Comm: blk_non_zero.st Not tainted 4.4.0-rc1+ #17
[  825.392056] Hardware name: HP ProLiant DL380 Gen9, BIOS P89 06/09/2015
[  825.424472] task: ffff880465bf6a40 ti: ffff88046133c000 task.ti: ffff88046133c000
[  825.461480] RIP: 0010:[<ffffffff81329856>]  [<ffffffff81329856>] strcmp+0x6/0x30
[  825.497916] RSP: 0000:ffff88046133fbc8  EFLAGS: 00000246
[  825.524836] RAX: 0000000000000000 RBX: ffff880c7fffd7c0 RCX: 000000076c800000
[  825.566847] RDX: 000000076c800fff RSI: ffffffff818ea1c8 RDI: ffffffff818ea1c8
[  825.605265] RBP: ffff88046133fbc8 R08: 0000000000000001 R09: ffff8804652300c0
[  825.643628] R10: 00007f1b4fe0b000 R11: ffff880465230228 R12: ffffffff818ea1bd
[  825.681381] R13: 0000000000000001 R14: ffff88046133fc20 R15: 0000000080000200
[  825.718607] FS:  00007f1b5102d880(0000) GS:ffff88046f8c0000(0000) knlGS:00000000000000
00
[  825.761663] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  825.792213] CR2: 00007f1b4fe0b000 CR3: 000000046b225000 CR4: 00000000001406e0
[  825.830906] Stack:
[  825.841235]  ffff88046133fc10 ffffffff81084610 000000076c800000 000000076c800fff
[  825.879533]  000000076c800fff 00000000ffffffff ffff88046133fc90 ffffffff8106d1d0
[  825.916774]  000000000000000c ffff88046133fc80 ffffffff81084f0d 000000076c800000
[  825.953220] Call Trace:
[  825.965386]  [<ffffffff81084610>] find_next_iomem_res+0xd0/0x130
[  825.996804]  [<ffffffff8106d1d0>] ? pat_enabled+0x20/0x20
[  826.024773]  [<ffffffff81084f0d>] walk_system_ram_range+0x8d/0xf0
[  826.055565]  [<ffffffff8106d2d8>] pat_pagerange_is_ram+0x78/0xa0
[  826.088971]  [<ffffffff8106d475>] lookup_memtype+0x35/0xc0
[  826.121385]  [<ffffffff8106e33b>] track_pfn_insert+0x2b/0x60
[  826.154600]  [<ffffffff811e5523>] vmf_insert_pfn_pmd+0xb3/0x210
[  826.187992]  [<ffffffff8124acab>] __dax_pmd_fault+0x3cb/0x610
[  826.221337]  [<ffffffffa0769910>] ? ext4_dax_mkwrite+0x20/0x20 [ext4]
[  826.259190]  [<ffffffffa0769a4d>] ext4_dax_pmd_fault+0xcd/0x100 [ext4]
[  826.293414]  [<ffffffff811b0af7>] handle_mm_fault+0x3b7/0x510
[  826.323763]  [<ffffffff81068f98>] __do_page_fault+0x188/0x3f0
[  826.358186]  [<ffffffff81069230>] do_page_fault+0x30/0x80
[  826.391212]  [<ffffffff8169c148>] page_fault+0x28/0x30
[  826.420752] Code: 89 e5 74 09 48 83 c2 01 80 3a 00 75 f7 48 83 c6 01 0f b6 4e ff 48 83
 c2 01 84 c9 88 4a ff 75 ed 5d c3 0f 1f 00 55 48 89 e5 eb 04 <84> c0 74 18 48 83 c7 01 0f
 b6 47 ff 48 83 c6 01 3a 46 ff 74 eb 

The full output is large (48 cpus), so I'm going to be lazy and not
cut-n-paste it here.

Cheers,
Jeff
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