Date:	Wed, 29 Jul 2015 11:32:06 -0400
From:	Ming Lei <ming.lei@...onical.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Josh Boyer <jwboyer@...oraproject.org>, Tejun Heo <tj@...nel.org>,
	Jens Axboe <axboe@...com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: cgroup/loop Bad page state oops in Linux v4.2-rc3-136-g45b4b782e848

On Wed, Jul 29, 2015 at 9:51 AM, Johannes Weiner <hannes@...xchg.org> wrote:
> On Wed, Jul 29, 2015 at 09:27:16AM -0400, Josh Boyer wrote:
>> Hi All,
>>
>> We've gotten a report[1] that any of the upcoming Fedora 23 install
>> images are all failing on 32-bit VMs/machines.  Looking at the first
>> instance of the oops, it seems to be a bad page state where a page is
>> still charged to a group and it is trying to be freed.  The oops
>> output is below.
>>
>> Has anyone seen this in their 32-bit testing at all?  Thus far nobody
>> can recreate this on a 64-bit machine/VM.
>>
>> josh
>>
>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1247382
>>
>> [    9.026738] systemd[1]: Switching root.
>> [    9.036467] systemd-journald[149]: Received SIGTERM from PID 1 (systemd).
>> [    9.082262] BUG: Bad page state in process kworker/u5:1  pfn:372ac
>> [    9.083989] page:f3d32ae0 count:0 mapcount:0 mapping:f2252178 index:0x16a
>> [    9.085755] flags: 0x40020021(locked|lru|mappedtodisk)
>> [    9.087284] page dumped because: page still charged to cgroup
>> [    9.088772] bad because of flags:
>> [    9.089731] flags: 0x21(locked|lru)
>> [    9.090818] page->mem_cgroup:f2c3e400
>
> It's also still locked and on the LRU. This page shouldn't have been
> freed.
>
>> [    9.117848] Call Trace:
>> [    9.118738]  [<c0aa22c9>] dump_stack+0x41/0x52
>> [    9.120034]  [<c054e30a>] bad_page.part.80+0xaa/0x100
>> [    9.121461]  [<c054eea9>] free_pages_prepare+0x3b9/0x3f0
>> [    9.122934]  [<c054fae2>] free_hot_cold_page+0x22/0x160
>> [    9.124400]  [<c071a22f>] ? copy_to_iter+0x1af/0x2a0
>> [    9.125750]  [<c054c4a3>] ? mempool_free_slab+0x13/0x20
>> [    9.126840]  [<c054fc57>] __free_pages+0x37/0x50
>> [    9.127849]  [<c054c4fd>] mempool_free_pages+0xd/0x10
>> [    9.128908]  [<c054c8b6>] mempool_free+0x26/0x80
>> [    9.129895]  [<c06f77e6>] bounce_end_io+0x56/0x80
>
> The page state looks completely off for a bounce buffer page. Did
> somebody mess with a bounce bio's bv_page?

Looks the page isn't touched in both lo_read_transfer() and
lo_read_simple().

Maybe it is related with aa4d86163e4e(block: loop: switch to VFS ITER_BVEC),
or it  might be helpful to run 'git bisect' if reverting aa4d86163e4e can't
fix the issue, suppose the issue can be reproduced easily.

>
>> [    9.130923]  [<c06f7ce2>] bounce_end_io_read+0x32/0x40
>> [    9.131973]  [<c06d8dc6>] bio_endio+0x56/0x90
>> [    9.132953]  [<c06df817>] blk_update_request+0x87/0x310
>> [    9.134042]  [<c04499f7>] ? kvm_clock_read+0x17/0x20
>> [    9.135103]  [<c040bdd8>] ? sched_clock+0x8/0x10
>> [    9.136100]  [<c06e7756>] blk_mq_end_request+0x16/0x60
>> [    9.136912]  [<c06e7fed>] __blk_mq_complete_request+0x9d/0xd0
>> [    9.137730]  [<c06e8035>] blk_mq_complete_request+0x15/0x20
>> [    9.138515]  [<f7e0851d>] loop_handle_cmd.isra.23+0x5d/0x8c0 [loop]
>> [    9.139390]  [<c0491b53>] ? pick_next_task_fair+0xa63/0xbb0
>> [    9.140202]  [<f7e08e60>] loop_queue_read_work+0x10/0x12 [loop]
>> [    9.141043]  [<c0471c55>] process_one_work+0x145/0x380
>> [    9.141779]  [<c0471ec9>] worker_thread+0x39/0x430
>> [    9.142524]  [<c0471e90>] ? process_one_work+0x380/0x380
>> [    9.143303]  [<c04772b6>] kthread+0xa6/0xc0
>> [    9.143936]  [<c0aa7a81>] ret_from_kernel_thread+0x21/0x30
>> [    9.144742]  [<c0477210>] ? kthread_worker_fn+0x130/0x130
>> [    9.145529] Disabling lock debugging due to kernel taint
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