From: Alexey Kardashevskiy aik@ozlabs.ru
[ Upstream commit cc7130bf119add37f36238343a593b71ef6ecc1e ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/iommu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c index 80b6caaa9b92..87af91937c8a 100644 --- a/arch/powerpc/kernel/iommu.c +++ b/arch/powerpc/kernel/iommu.c @@ -1055,7 +1055,7 @@ 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);
if (tbl->it_offset == 0) clear_bit(0, tbl->it_map); @@ -1084,7 +1084,7 @@ 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);