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

[Baolu Lu <baolu.lu@linux.intel.com>]

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.

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);

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