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Date: Mon, 30 Jan 2023 14:59:00 +0000
From: Robin Murphy <robin.murphy@....com>
To: Baolu Lu <baolu.lu@...ux.intel.com>, joro@...tes.org,
will@...nel.org
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, hch@....de,
jgg@...dia.com
Subject: Re: [PATCH v2 3/8] iommu: Add lockdep annotations for group list
iterators
On 2023-01-28 12:20, Baolu Lu wrote:
> On 2023/1/27 2:26, Robin Murphy wrote:
>> Before we add any more common helpers for iterating or otherwise
>> accessing the group device list, let's start the good habit of
>> annotating their locking expectations for robustness.
>>
>> Signed-off-by: Robin Murphy <robin.murphy@....com>
>> ---
>>
>> v2: New. Note that I've left the group_pasid helpers, since they're
>> pretty much right next to where the relevant locking happens, and
>> highly unlikely to be reused from anywhere else anyway.
>>
>> drivers/iommu/iommu.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index d48e5499e0fa..77f076030995 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -20,6 +20,7 @@
>> #include <linux/iommu.h>
>> #include <linux/idr.h>
>> #include <linux/err.h>
>> +#include <linux/lockdep.h>
>> #include <linux/pci.h>
>> #include <linux/pci-ats.h>
>> #include <linux/bitops.h>
>> @@ -1100,6 +1101,7 @@ static int iommu_group_device_count(struct
>> iommu_group *group)
>> struct group_device *entry;
>> int ret = 0;
>> + lockdep_assert_held(&group->mutex);
>> list_for_each_entry(entry, &group->devices, list)
>> ret++;
>> @@ -1112,6 +1114,7 @@ static int __iommu_group_for_each_dev(struct
>> iommu_group *group, void *data,
>> struct group_device *device;
>> int ret = 0;
>> + lockdep_assert_held(&group->mutex);
>
> When I tested this patch on an Intel platform, I found that the
> bus_iommu_probe() path iterates the group device list but does not hold
> the lock.
Urgh, that's what I get for being in a hurry and not boot-testing it
myself :(
> 1831 static void __iommu_group_dma_finalize(struct iommu_group *group)
> 1832 {
> 1833 __iommu_group_for_each_dev(group, group->default_domain,
> 1834 iommu_group_do_probe_finalize);
> 1835 }
>
> bus_iommu_probe:
>
> 1873 /* Try to allocate default domain */
> 1874 probe_alloc_default_domain(group);
> 1875
> 1876 if (!group->default_domain) {
> 1877 mutex_unlock(&group->mutex);
> 1878 continue;
> 1879 }
> 1880
> 1881 iommu_group_create_direct_mappings(group);
> 1882
> 1883 ret = __iommu_group_dma_first_attach(group);
> 1884
> 1885 mutex_unlock(&group->mutex);
> 1886
> 1887 if (ret)
> 1888 break;
> 1889
> 1890 __iommu_group_dma_finalize(group);
...and of course it's the one case where the reason for not holding the
lock is a bit dodgy, but most definitely intentional. I can see ways to
hack around it further, but frankly I think the most practical solution
would be to just drop this patch for now until I've sorted out the ARM
stuff.
Thanks,
Robin.
> The lockdep_assert_held() caused below kernel trace:
>
> [ 70.022590] ------------[ cut here ]------------
> [ 70.027967] WARNING: CPU: 1 PID: 1 at drivers/iommu/iommu.c:1135
> __iommu_group_for_each_dev+0x72/0x80
> [ 70.038672] Modules linked in:
> [ 70.042264] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G W
> 6.2.0-rc5+ #421
> [ 70.063860] RIP: 0010:__iommu_group_for_each_dev+0x72/0x80
> [ 70.070267] Code: 5c 41 5d c3 cc cc cc cc 5b 31 c0 5d 41 5c 41 5d c3
> cc cc cc cc 48 8d bf 10 01 00 00 be ff ff ff ff e8 92 7b 8f 00 85 c0 75
> ac <0f> 0b eb a8 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90
> [ 70.091981] RSP: 0000:ffffad104006fd30 EFLAGS: 00010246
> [ 70.098058] RAX: 0000000000000000 RBX: ffff9f490bb95600 RCX:
> 0000000000000001
> [ 70.106378] RDX: 0000000000000001 RSI: ffff9f490bb95710 RDI:
> ffff9f4900b10d88
> [ 70.114674] RBP: ffff9f490bb95600 R08: ffffcd26844fde80 R09:
> ffffcd26844fde40
> [ 70.122970] R10: 0000000000000000 R11: 0000000000000000 R12:
> ffff9f490bb95ed0
> [ 70.131265] R13: ffffffff8aadd520 R14: ffffffff8aade3a0 R15:
> 0000000000000000
> [ 70.139561] FS: 0000000000000000(0000) GS:ffff9f583ff00000(0000)
> knlGS:0000000000000000
> [ 70.148969] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 70.155667] CR2: 0000000000000000 CR3: 0000000cc2012001 CR4:
> 0000000000370ee0
> [ 70.163963] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [ 70.172282] DR3: 0000000000000000 DR6: 00000000ffff07f0 DR7:
> 0000000000000400
> [ 70.180559] Call Trace:
> [ 70.183469] <TASK>
> [ 70.185972] bus_iommu_probe+0xee/0x1e0
> [ 70.190496] iommu_device_register+0xaf/0x100
> [ 70.195580] intel_iommu_init+0x3e9/0x6f2
> [ 70.200271] ? __pfx_pci_iommu_init+0x10/0x10
> [ 70.205381] ? __pfx_ignore_unknown_bootoption+0x10/0x10
> [ 70.211564] pci_iommu_init+0x12/0x3a
> [ 70.215870] do_one_initcall+0x65/0x330
> [ 70.220376] ? __pfx_ignore_unknown_bootoption+0x10/0x10
> [ 70.226577] ? rcu_read_lock_sched_held+0x5a/0x80
> [ 70.232076] kernel_init_freeable+0x287/0x2f0
> [ 70.237914] ? __pfx_kernel_init+0x10/0x10
> [ 70.241979] kernel_init+0x1a/0x130
> [ 70.246075] ret_from_fork+0x29/0x50
> [ 70.251014] </TASK>
> [ 70.252867] irq event stamp: 16350051
> [ 70.257167] hardirqs last enabled at (16350061):
> [<ffffffff8a1c3ed2>] __up_console_sem+0x52/0x60
> [ 70.267468] hardirqs last disabled at (16350070):
> [<ffffffff8a1c3eb7>] __up_console_sem+0x37/0x60
> [ 70.277768] softirqs last enabled at (16350006):
> [<ffffffff8b3edd03>] __do_softirq+0x283/0x451
> [ 70.287859] softirqs last disabled at (16350001):
> [<ffffffff8a132c6a>] irq_exit_rcu+0xaa/0xc0
> [ 70.297777] ---[ end trace 0000000000000000 ]---
>
>> list_for_each_entry(device, &group->devices, list) {
>> ret = fn(device->dev, data);
>> if (ret)
>
> Best regards,
> baolu
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