Re: [PATCH v2 3/8] iommu: Add lockdep annotations for group list iterators

Robin Murphy
2023-01-30T14:59:14Z

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@arm.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