It is safe to traverse mm->context.iommu_group_mem_list with either
mem_list_mutex or the RCU read lock held. Silence a few RCU-list false
positive warnings and fix a few missing RCU read locks.
arch/powerpc/mm/book3s64/iommu_api.c:330 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
2 locks held by qemu-kvm/4305:
#0: c000000bc3fe4d68 (&container->lock){+.+.}-{3:3}, at: tce_iommu_ioctl.part.9+0xc7c/0x1870 [vfio_iommu_spapr_tce]
#1: c000000001501910 (mem_list_mutex){+.+.}-{3:3}, at: mm_iommu_get+0x50/0x190
====
arch/powerpc/mm/book3s64/iommu_api.c:132 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
2 locks held by qemu-kvm/4305:
#0: c000000bc3fe4d68 (&container->lock){+.+.}-{3:3}, at: tce_iommu_ioctl.part.9+0xc7c/0x1870 [vfio_iommu_spapr_tce]
#1: c000000001501910 (mem_list_mutex){+.+.}-{3:3}, at: mm_iommu_do_alloc+0x120/0x5f0
====
arch/powerpc/mm/book3s64/iommu_api.c:292 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
2 locks held by qemu-kvm/4312:
#0: c000000ecafe23c8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0xdc/0x950 [kvm]
#1: c000000045e6c468 (&kvm->srcu){....}-{0:0}, at: kvmppc_h_put_tce+0x88/0x340 [kvm]
====
arch/powerpc/mm/book3s64/iommu_api.c:424 RCU-list traversed in non-reader section!!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
2 locks held by qemu-kvm/4312:
#0: c000000ecafe23c8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0xdc/0x950 [kvm]
#1: c000000045e6c468 (&kvm->srcu){....}-{0:0}, at: kvmppc_h_put_tce+0x88/0x340 [kvm]
Signed-off-by: Qian Cai <[email protected]>
---
arch/powerpc/mm/book3s64/iommu_api.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
index fa05bbd1f682..bf0108b6f445 100644
--- a/arch/powerpc/mm/book3s64/iommu_api.c
+++ b/arch/powerpc/mm/book3s64/iommu_api.c
@@ -129,7 +129,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
mutex_lock(&mem_list_mutex);
- list_for_each_entry_rcu(mem2, &mm->context.iommu_group_mem_list, next) {
+ list_for_each_entry_rcu(mem2, &mm->context.iommu_group_mem_list, next,
+ lockdep_is_held(&mem_list_mutex)) {
/* Overlap? */
if ((mem2->ua < (ua + (entries << PAGE_SHIFT))) &&
(ua < (mem2->ua +
@@ -289,6 +290,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_lookup(struct mm_struct *mm,
{
struct mm_iommu_table_group_mem_t *mem, *ret = NULL;
+ rcu_read_lock();
list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
if ((mem->ua <= ua) &&
(ua + size <= mem->ua +
@@ -297,6 +299,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_lookup(struct mm_struct *mm,
break;
}
}
+ rcu_read_unlock();
return ret;
}
@@ -327,7 +330,8 @@ struct mm_iommu_table_group_mem_t *mm_iommu_get(struct mm_struct *mm,
mutex_lock(&mem_list_mutex);
- list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
+ list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next,
+ lockdep_is_held(&mem_list_mutex)) {
if ((mem->ua == ua) && (mem->entries == entries)) {
ret = mem;
++mem->used;
@@ -421,6 +425,7 @@ bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
struct mm_iommu_table_group_mem_t *mem;
unsigned long end;
+ rcu_read_lock();
list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, next) {
if (mem->dev_hpa == MM_IOMMU_TABLE_INVALID_HPA)
continue;
@@ -437,6 +442,7 @@ bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
return true;
}
}
+ rcu_read_unlock();
return false;
}
--
2.21.0 (Apple Git-122.2)
On Sun, 10 May 2020 01:15:59 -0400, Qian Cai wrote:
> It is safe to traverse mm->context.iommu_group_mem_list with either
> mem_list_mutex or the RCU read lock held. Silence a few RCU-list false
> positive warnings and fix a few missing RCU read locks.
>
> arch/powerpc/mm/book3s64/iommu_api.c:330 RCU-list traversed in non-reader section!!
>
> other info that might help us debug this:
>
> [...]
Applied to powerpc/next.
[1/1] powerpc/mm/book3s64/iommu: fix some RCU-list locks
https://git.kernel.org/powerpc/c/b5952f8125ae512420d5fc569adce591bea73bf5
cheers