Re: [PATCH] iommu/vt-d: Remove unnecessary locking in intel_irq_remapping_alloc()

[Baolu Lu]

On 4/27/23 8:43 AM, Nicolin Chen wrote:
> Hi Baolu/Jason,

Hi Nicolin,

> On Mon, Mar 27, 2023 at 06:13:10AM -0700, Baolu Lu wrote:
> > On 2023/3/27 20:18, Jason Gunthorpe wrote:
> > > On Tue, Mar 14, 2023 at 01:18:36PM +0800, Lu Baolu wrote:
> > > > The global rwsem dmar_global_lock was introduced by commit 3a5670e8ac932
> > > > ("iommu/vt-d: Introduce a rwsem to protect global data structures"). It
> > > > is used to protect DMAR related global data from DMAR hotplug operations.
> > > >
> > > > Using dmar_global_lock in intel_irq_remapping_alloc() is unnecessary as
> > > > the DMAR global data structures are not touched there. Remove it to avoid
> > > > below lockdep warning.
> > >
> > > Tested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > >
> > > Solves my splat too
> > >
> > > Let's send this to -rc please
> >
> > Thank you for the testing. I will queue it for Joerg this week.
>
> I found a couple of kernel warnings switching from v6.3-rc4
> to v6.3-rc5. Git-bisect is pointing at this commit.
>
> My test environment is MKT enabling irq_remap:
> https://github.com/Mellanox/mkt
> CONFIG_IOMMUFD=m
> CONFIG_IOMMUFD_VFIO_CONTAINER=y
> CONFIG_IOMMUFD_TEST=y
> CONFIG_IRQ_REMAP=y
>
> Any idea?
>
> Thanks
> Nicolin
>
> Attaching WARNINGs:
> [   19.680725] ------------[ cut here ]------------
> [   19.681083] WARNING: CPU: 0 PID: 561 at include/linux/mmap_lock.h:161 track_pfn_remap+0xf5/0x100
> [   19.681356] Modules linked in: vfio_pci vfio_pci_core irqbypass vfio iommufd mlx5_ib ib_uverbs ib_core mlx5_core
> [   19.681654] CPU: 0 PID: 561 Comm: python3 Not tainted 6.3.0-rc6+ #1080
> [   19.681808] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> [   19.682108] RIP: 0010:track_pfn_remap+0xf5/0x100
> [   19.682270] Code: 5e 5d c3 48 89 f2 31 c9 4c 89 c6 4c 89 e7 e8 42 fc ff ff e9 54 ff ff ff 48 8d b8 88 01 00 00 31 f6 e8 5f 97 76 00 85 c0 75 be <0f> 0b eb ba 0f 1f 80 00 00 00 00 80 3d 71 72 ef 00 00 74 01 c3 55
> [   19.682678] RSP: 0000:ffffc900014b7ce8 EFLAGS: 00010246
> [   19.682805] RAX: 0000000000000000 RBX: 0000000002000000 RCX: 0000000000000000
> [   19.682984] RDX: 0000000000000000 RSI: ffff888104a709c8 RDI: ffff888108756150
> [   19.683214] RBP: ffffc900014b7d08 R08: 0000000000000001 R09: 0000000000000003
> [   19.683464] R10: 000000000e6a4a47 R11: 00000000620892b1 R12: 00000000fc000000
> [   19.683663] R13: ffffc900014b7d20 R14: ffff888106a35100 R15: 0000000002000000
> [   19.683843] FS:  00007fa8aa4edb80(0000) GS:ffff8881ba400000(0000) knlGS:0000000000000000
> [   19.684054] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   19.684223] CR2: 00007fa8a748f004 CR3: 000000010673b005 CR4: 00000000003706b0
> [   19.684414] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [   19.684632] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [   19.684817] Call Trace:
> [   19.684893]  <TASK>
> [   19.684967]  remap_pfn_range+0x3e/0xa0
> [   19.685084]  vfio_pci_mmap_fault+0x8a/0x160 [vfio_pci_core]
> [   19.685253]  __do_fault+0x30/0xa0
> [   19.685368]  __handle_mm_fault+0xe08/0x1ff0
> [   19.685520]  ? find_held_lock+0x31/0x80
> [   19.685655]  ? mt_find+0x15d/0x400
> [   19.685759]  ? lock_release+0xbc/0x240
> [   19.685862]  handle_mm_fault+0xa8/0x170
> [   19.685963]  ? find_vma+0x3c/0x70
> [   19.686066]  exc_page_fault+0x1e6/0x7b0
> [   19.686167]  asm_exc_page_fault+0x27/0x30
> [   19.686271] RIP: 0033:0x7fa8a986bfd5
> [   19.686373] Code: ef 41 89 c4 e8 dc 70 fc ff 45 85 e4 0f 85 a0 0e 00 00 48 89 df e8 3b ce ff ff 48 85 c0 0f 84 eb 0d 00 00 48 8b ab e8 02 00 00 <8b> 45 04 0f c8 c1 e8 10 83 f8 05 0f 85 b0 0b 00 00 8b 45 14 ba 01
> [   19.686773] RSP: 002b:00007ffc2392ab30 EFLAGS: 00010206
> [   19.686931] RAX: 0000559646201590 RBX: 0000559646471a50 RCX: 0000559646471d00
> [   19.687132] RDX: 0000559646471d00 RSI: 0000000000003b71 RDI: 0000000000000003
> [   19.687377] RBP: 00007fa8a748f000 R08: 00000000fedfffff R09: 0000000000000000
> [   19.687563] R10: 0000000000000022 R11: 0000000000000246 R12: 0000559646470904
> [   19.687744] R13: 00007ffc2392ab70 R14: 0000000000000002 R15: 0000559646470934
> [   19.687943]  </TASK>
> [   19.688016] irq event stamp: 655597
> [   19.688114] hardirqs last  enabled at (655605): [<ffffffff810c9683>] __up_console_sem+0x53/0x60
> [   19.688340] hardirqs last disabled at (655612): [<ffffffff810c9668>] __up_console_sem+0x38/0x60
> [   19.688554] softirqs last  enabled at (655148): [<ffffffff81064e79>] irq_exit_rcu+0x69/0x90
> [   19.688733] softirqs last disabled at (655143): [<ffffffff81064e79>] irq_exit_rcu+0x69/0x90
> [   19.688915] ---[ end trace 0000000000000000 ]---
> [   19.689076] ------------[ cut here ]------------
> [   19.689197] WARNING: CPU: 0 PID: 561 at include/linux/mmap_lock.h:161 remap_pfn_range_notrack+0x40f/0x4f0
> [   19.689440] Modules linked in: vfio_pci vfio_pci_core irqbypass vfio iommufd mlx5_ib ib_uverbs ib_core mlx5_core
> [   19.689691] CPU: 0 PID: 561 Comm: python3 Tainted: G        W          6.3.0-rc6+ #1080
> [   19.689867] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> [   19.690109] RIP: 0010:remap_pfn_range_notrack+0x40f/0x4f0
> [   19.690234] Code: 39 eb 0f 85 d9 fc ff ff 31 c0 eb 5e 48 8b 45 a8 31 f6 4c 89 45 d0 48 8d b8 88 01 00 00 e8 89 bc 5a 00 4c 8b 45 d0 85 c0 75 02 <0f> 0b 48 8b 43 20 e9 5e fc ff ff 48 8b 7d a8 48 89 c6 48 89 c3 e8
> [   19.690628] RSP: 0000:ffffc900014b7c68 EFLAGS: 00010246
> [   19.690750] RAX: 0000000000000000 RBX: ffff888106a35100 RCX: 0000000000000000
> [   19.690914] RDX: 0000000000000000 RSI: ffff888104a709c8 RDI: ffff888108756150
> [   19.691074] RBP: ffffc900014b7d08 R08: 00007fa8a948f000 R09: 0000000000000003
> [   19.691274] R10: 000000000e6a4a47 R11: 00000000620892b1 R12: 00000000000fc000
> [   19.691469] R13: 00007fa8a748f000 R14: 00007fa8a748f000 R15: 8000000000000037
> [   19.691647] FS:  00007fa8aa4edb80(0000) GS:ffff8881ba400000(0000) knlGS:0000000000000000
> [   19.691830] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   19.691980] CR2: 00007fa8a748f004 CR3: 000000010673b005 CR4: 00000000003706b0
> [   19.692159] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [   19.692336] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [   19.692538] Call Trace:
> [   19.692592]  <TASK>
> [   19.692647]  ? track_pfn_remap+0xf7/0x100
> [   19.692745]  remap_pfn_range+0x57/0xa0
> [   19.692845]  vfio_pci_mmap_fault+0x8a/0x160 [vfio_pci_core]
> [   19.692991]  __do_fault+0x30/0xa0
> [   19.693089]  __handle_mm_fault+0xe08/0x1ff0
> [   19.693186]  ? find_held_lock+0x31/0x80
> [   19.693291]  ? mt_find+0x15d/0x400
> [   19.693391]  ? lock_release+0xbc/0x240
> [   19.693491]  handle_mm_fault+0xa8/0x170
> [   19.693587]  ? find_vma+0x3c/0x70
> [   19.693685]  exc_page_fault+0x1e6/0x7b0
> [   19.693782]  asm_exc_page_fault+0x27/0x30
> [   19.693880] RIP: 0033:0x7fa8a986bfd5
> [   19.693961] Code: ef 41 89 c4 e8 dc 70 fc ff 45 85 e4 0f 85 a0 0e 00 00 48 89 df e8 3b ce ff ff 48 85 c0 0f 84 eb 0d 00 00 48 8b ab e8 02 00 00 <8b> 45 04 0f c8 c1 e8 10 83 f8 05 0f 85 b0 0b 00 00 8b 45 14 ba 01
> [   19.694342] RSP: 002b:00007ffc2392ab30 EFLAGS: 00010206
> [   19.694466] RAX: 0000559646201590 RBX: 0000559646471a50 RCX: 0000559646471d00
> [   19.694619] RDX: 0000559646471d00 RSI: 0000000000003b71 RDI: 0000000000000003
> [   19.694778] RBP: 00007fa8a748f000 R08: 00000000fedfffff R09: 0000000000000000
> [   19.694934] R10: 0000000000000022 R11: 0000000000000246 R12: 0000559646470904
> [   19.695092] R13: 00007ffc2392ab70 R14: 0000000000000002 R15: 0000559646470934
> [   19.695302]  </TASK>
> [   19.695373] irq event stamp: 656049
> [   19.695452] hardirqs last  enabled at (656057): [<ffffffff810c9683>] __up_console_sem+0x53/0x60
> [   19.695657] hardirqs last disabled at (656064): [<ffffffff810c9668>] __up_console_sem+0x38/0x60
> [   19.695883] softirqs last  enabled at (655148): [<ffffffff81064e79>] irq_exit_rcu+0x69/0x90
> [   19.696061] softirqs last disabled at (655143): [<ffffffff81064e79>] irq_exit_rcu+0x69/0x90
> [   19.696240] ---[ end trace 0000000000000000 ]---

I took a quick look. It seems that above warnings are irrelevant to this
commit. Can you please simply revert this commit and check whether there
are any changes?

Best regards,
baolu