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

From: Baolu Lu
Date: Sat Jan 28 2023 - 07:21:47 EST

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@xxxxxxx>
---

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