In general, if swiotlb is sufficient, the logic of index =
wrap_area_index(mem, index + 1) is fine, it will quickly take a slot and
release the area->lock; But if swiotlb is insufficient and the device
has min_align_mask requirements, such as NVME, we may not be able to
satisfy index == wrap and exit the loop properly. In this case, other
kernel threads will not be able to acquire the area->lock and release
the slot, resulting in a deadlock.
The current implementation of wrap_area_index does not involve a modulo
operation, so adjusting the wrap to ensure the loop ends is not trivial.
Introduce the index_nowrap variable to record the number of loops and
exit the loop after completing the traversal.
Backtraces:
Other CPUs are waiting this core to exit the swiotlb_do_find_slots
loop.
[10199.924391] RIP: 0010:swiotlb_do_find_slots+0x1fe/0x3e0
[10199.924403] Call Trace:
[10199.924404] <TASK>
[10199.924405] swiotlb_tbl_map_single+0xec/0x1f0
[10199.924407] swiotlb_map+0x5c/0x260
[10199.924409] ? nvme_pci_setup_prps+0x1ed/0x340
[10199.924411] dma_direct_map_page+0x12e/0x1c0
[10199.924413] nvme_map_data+0x304/0x370
[10199.924415] nvme_prep_rq.part.0+0x31/0x120
[10199.924417] nvme_queue_rq+0x77/0x1f0
...
[ 9639.596311] NMI backtrace for cpu 48
[ 9639.596336] Call Trace:
[ 9639.596337]
[ 9639.596338] _raw_spin_lock_irqsave+0x37/0x40
[ 9639.596341] swiotlb_do_find_slots+0xef/0x3e0
[ 9639.596344] swiotlb_tbl_map_single+0xec/0x1f0
[ 9639.596347] swiotlb_map+0x5c/0x260
[ 9639.596349] dma_direct_map_sg+0x7a/0x280
[ 9639.596352] __dma_map_sg_attrs+0x30/0x70
[ 9639.596355] dma_map_sgtable+0x1d/0x30
[ 9639.596356] nvme_map_data+0xce/0x370
...
[ 9639.595665] NMI backtrace for cpu 50
[ 9639.595682] Call Trace:
[ 9639.595682]
[ 9639.595683] _raw_spin_lock_irqsave+0x37/0x40
[ 9639.595686] swiotlb_release_slots.isra.0+0x86/0x180
[ 9639.595688] dma_direct_unmap_sg+0xcf/0x1a0
[ 9639.595690] nvme_unmap_data.part.0+0x43/0xc0
Fixes: 1f221a0d0dbf ("swiotlb: respect min_align_mask")
Signed-off-by: GuoRui.Yu <GuoRui.Yu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Xiaokang Hu <xiaokang.hxk@xxxxxxxxxxxxxxx>
---
kernel/dma/swiotlb.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index a34c38bbe28f..638ba3ea94f4 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -632,7 +632,7 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
unsigned int iotlb_align_mask =
dma_get_min_align_mask(dev) & ~(IO_TLB_SIZE - 1);
unsigned int nslots = nr_slots(alloc_size), stride;
- unsigned int index, wrap, count = 0, i;
+ unsigned int index, index_nowrap = 0, wrap, count = 0, i;
unsigned int offset = swiotlb_align_offset(dev, orig_addr);
unsigned long flags;
unsigned int slot_base;
@@ -665,6 +665,7 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
(slot_addr(tbl_dma_addr, slot_index) &
iotlb_align_mask) != (orig_addr & iotlb_align_mask)) {
index = wrap_area_index(mem, index + 1);
+ index_nowrap++;
continue;
}
@@ -680,7 +681,8 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
goto found;
}
index = wrap_area_index(mem, index + stride);
- } while (index != wrap);
+ index_nowrap += stride;
+ } while (index_nowrap < mem->area_nslabs);
not_found:
spin_unlock_irqrestore(&area->lock, flags);
--
2.31.1
