RE: [bug report] Commit ccf953d8f3d6 ("fb_defio: Remove custom address_space_operations") breaks Hyper-V FB driver

[Dexuan Cui <decui@microsoft.com>]

> From: Dexuan Cui
> Sent: Friday, June 4, 2021 11:17 AM
> > >> ...
> > > I've heard a similar report from Vineeth but we didn't get to the bottom
> > > of this.
> > I have just tried reverting the commit mentioned above and it solves the
> > GUI freeze
> > I was also seeing. Previously, login screen was just freezing, but VM
> > was accessible
> > through ssh. With the above commit reverted, I can login to Gnome.
> >
> > Looks like I am also experiencing the same bug mentioned here.
> >
> > Thanks,
> > Vineeth
> 
> As Matthew mentioned, this is a known issue:
> https://lwn.net/ml/linux-kernel/YLZEhv0cpZp8uVE3@casper.infradead.org/
> 
> Matthew has reverted ccf953d8f3d6:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=
> 0b78f8bcf4951af30b0ae83ea4fad27d641ab617
> so the latest mainline should work now.
> 
> Thanks,
> Dexuan

Hi Matthew,
With today's latest mainline 16f0596fc1d78a1f3ae4628cff962bb297dc908c,
the Xorg works again in Linux VM on Hyper-V, but when I reboot the VM, I
always see a lot of "BUG: Bad page state in process Xorg " warnings (there
are about 60 such warnings) before the VM reboots.

BTW, I happen to have an older Mar-28 mainline kernel (36a14638f7c0654),
which has the same warnings. 

Any idea which change introduced the warnings? 

[   87.446129] BUG: Bad page state in process Xorg  pfn:151807
[   87.448238] page:000000004f982270 refcount:0 mapcount:0 mapping:00000000dcf68290 index:0x0 pfn:0x151807
[   87.455506] aops:fb_deferred_io_aops ino:f9 dentry name:"fb0"
[   87.455506] flags: 0x57fffc000000000(node=1|zone=2|lastcpupid=0x1ffff)
[   87.455506] raw: 057fffc000000000 dead000000000100 dead000000000122 ffff9fa811c4a280
[   87.455506] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[   87.455506] page dumped because: non-NULL mapping
[   87.487491] Modules linked in: ...
[   87.491504] CPU: 6 PID: 1388 Comm: Xorg Tainted: G            E     5.13.0-rc4+ #1
[   87.533204] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090008  12/07/2018
[   87.533204] Call Trace:
[   87.533204]  dump_stack+0x64/0x7c
[   87.533204]  bad_page.cold.118+0x63/0x93
[  OK     87.533204]  free_pcppages_bulk+0x1ac/0x770
0m] Stopped Crea[   87.533204]  free_unref_page_list+0x101/0x180
te final runtime[   87.533204]  release_pages+0x186/0x4c0
[   87.533204]  tlb_flush_mmu+0x44/0x120
 dir for shutdow[   87.533204]  tlb_finish_mmu+0x3c/0x70
n pivot root.
[   87.533204]  unmap_region+0xd1/0x110
[   87.533204]  __do_munmap+0x2a2/0x500
[   87.533204]  __vm_munmap+0x7d/0x130
[   87.533204]  __x64_sys_munmap+0x27/0x30
[   87.533204]  do_syscall_64+0x3c/0xb0
[   87.533204]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[   87.533204] RIP: 0033:0x7f22b49a7567
[   87.533204] Code: 10 e9 67 ff ff ff 0f 1f 44 00 00 48 8b 15 21 ...
[   87.533204] RSP: 002b:00007ffd56c4f2b8 EFLAGS: 00000206 ORIG_RAX: 000000000000000b
[   87.533204] RAX: ffffffffffffffda RBX: 0000557f7299e200 RCX: 00007f22b49a7567
[   87.533204] RDX: 0000000000000000 RSI: 0000000000400000 RDI: 00007f22b3652000
[   87.533204] RBP: 0000557f7299edf0 R08: 0000557f729abfc0 R09: 0000000000000005
[   87.533204] R10: 0000000000000034 R11: 0000000000000206 R12: 0000557f7299edf0
[   87.533204] R13: 0000000000000000 R14: 0000557f71cf6968 R15: 0000557f71cdbe10
[   87.533204] Disabling lock debugging due to kernel taint
[   87.533204] BUG: Bad page state in process Xorg  pfn:151806
[   87.533204] page:00000000cf964098 refcount:0 mapcount:0 mapping:00000000dcf68290 index:0x0 pfn:0x151806
[   87.533204] aops:fb_deferred_io_aops ino:f9 dentry name:"fb0"
[   87.533204] flags: 0x57fffc000000000(node=1|zone=2|lastcpupid=0x1ffff)
[   87.533204] raw: 057fffc000000000 dead000000000100 dead000000000122 ffff9fa811c4a280
[   87.533204] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[   87.533204] page dumped because: non-NULL mapping
[   87.533204] Modules linked in: ...
[   87.533204] CPU: 6 PID: 1388 Comm: Xorg Tainted: G    B       E     5.13.0-rc4+ #1
[   87.533204] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090008  12/07/2018
[   87.747523] Call Trace:
[   87.747523]  dump_stack+0x64/0x7c
[   87.747523]  bad_page.cold.118+0x63/0x93
[   87.747523]  free_pcppages_bulk+0x1ac/0x770
[   87.747523]  free_unref_page_list+0x101/0x180
[   87.747523]  release_pages+0x186/0x4c0
[   87.747523]  tlb_flush_mmu+0x44/0x120
[   87.747523]  tlb_finish_mmu+0x3c/0x70
[   87.747523]  unmap_region+0xd1/0x110
[   87.747523]  __do_munmap+0x2a2/0x500
[   87.747523]  __vm_munmap+0x7d/0x130
[   87.747523]  __x64_sys_munmap+0x27/0x30
[   87.747523]  do_syscall_64+0x3c/0xb0
[   87.747523]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[   87.747523] RIP: 0033:0x7f22b49a7567
[   87.747523] Code: 10 e9 67 ff ff ff 0f 1f 44 00 00 48 8b 15 21 ...
[   87.747523] RSP: 002b:00007ffd56c4f2b8 EFLAGS: 00000206 ORIG_RAX: 000000000000000b
[   87.747523] RAX: ffffffffffffffda RBX: 0000557f7299e200 RCX: 00007f22b49a7567
[   87.747523] RDX: 0000000000000000 RSI: 0000000000400000 RDI: 00007f22b3652000
[   87.747523] RBP: 0000557f7299edf0 R08: 0000557f729abfc0 R09: 0000000000000005
[   87.747523] R10: 0000000000000034 R11: 0000000000000206 R12: 0000557f7299edf0
[   87.747523] R13: 0000000000000000 R14: 0000557f71cf6968 R15: 0000557f71cdbe10