powerpc/iommu: Annotate nested lock for lockdep

The IOMMU table is divided into pools for concurrent mappings and each
pool has a separate spinlock. When taking the ownership of an IOMMU group
to pass through a device to a VM, we lock these spinlocks which triggers
a false negative warning in lockdep (below).

This fixes it by annotating the large pool's spinlock as a nest lock
which makes lockdep not complaining when locking nested locks if
the nest lock is locked already.

===
WARNING: possible recursive locking detected
5.11.0-le_syzkaller_a+fstn1 #100 Not tainted
--------------------------------------------
qemu-system-ppc/4129 is trying to acquire lock:
c0000000119bddb0 (&(p->lock)/1){....}-{2:2}, at: iommu_take_ownership+0xac/0x1e0

but task is already holding lock:
c0000000119bdd30 (&(p->lock)/1){....}-{2:2}, at: iommu_take_ownership+0xac/0x1e0

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&(p->lock)/1);
  lock(&(p->lock)/1);
===

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210301063653.51003-1-aik@ozlabs.ru

diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
index 42e195aaf23a19723906a64895c475f9e8a7492b..560be519ad05100eae1172d2661e374b75aff074 100644 (file)
--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -1088,7 +1088,7 @@ int iommu_take_ownership(struct iommu_table *tbl)
 
        spin_lock_irqsave(&tbl->large_pool.lock, flags);
        for (i = 0; i < tbl->nr_pools; i++)
-               spin_lock(&tbl->pools[i].lock);
+               spin_lock_nest_lock(&tbl->pools[i].lock, &tbl->large_pool.lock);
 
        iommu_table_release_pages(tbl);
 
@@ -1116,7 +1116,7 @@ void iommu_release_ownership(struct iommu_table *tbl)
 
        spin_lock_irqsave(&tbl->large_pool.lock, flags);
        for (i = 0; i < tbl->nr_pools; i++)
-               spin_lock(&tbl->pools[i].lock);
+               spin_lock_nest_lock(&tbl->pools[i].lock, &tbl->large_pool.lock);
 
        memset(tbl->it_map, 0, sz);