Messages in this thread Patch in this message | | | From | Marek Szyprowski <> | Subject | [PATCH v2] arm: dma-mapping: fix potential endless loop in __dma_page_dev_to_cpu() | Date | Wed, 9 Aug 2023 19:27:37 +0200 |
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The D-cache cleaning loop should not call folio_next() beyond the requested region and rely on its parameters. Simply stop looping if left counter reaches zero.
This fixes the following endless loop observed by RCU stall on the ARM 32bit Exynos5422-based Odroid-XU3lite board:
--->8--- rcu: INFO: rcu_sched self-detected stall on CPU rcu: 0-....: (27320 ticks this GP) idle=e414/1/0x40000002 softirq=36/36 fqs=13044 rcu: (t=27385 jiffies g=-1067 q=34 ncpus=8) CPU: 0 PID: 93 Comm: kworker/0:1H Not tainted 6.5.0-rc5-next-20230807 #6981 Hardware name: Samsung Exynos (Flattened Device Tree) Workqueue: mmc_complete mmc_blk_mq_complete_work PC is at _set_bit+0x28/0x44 LR is at __dma_page_dev_to_cpu+0xdc/0x170 .. _set_bit from __dma_page_dev_to_cpu+0xdc/0x170 __dma_page_dev_to_cpu from dma_direct_unmap_sg+0x100/0x130 dma_direct_unmap_sg from dw_mci_post_req+0x68/0x6c dw_mci_post_req from mmc_blk_mq_post_req+0x34/0x100 mmc_blk_mq_post_req from mmc_blk_mq_complete_work+0x50/0x60 mmc_blk_mq_complete_work from process_one_work+0x20c/0x4d8 process_one_work from worker_thread+0x58/0x54c worker_thread from kthread+0xe0/0xfc kthread from ret_from_fork+0x14/0x2c --->8---
While touching this code, move the set_bit() operation, which deals with atomics, a bit up in the call chain. The new order helps a bit compiler to produce code computing folio_size() only once.
Fixes: cc24e9c0895c ("arm: implement the new page table range API") Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- v2: - changed the code and explaiation as suggested by Russell and Matthew
v1: - https://lore.kernel.org/all/20230807152657.1692414-1-m.szyprowski@samsung.com/ --- arch/arm/mm/dma-mapping.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c index 70cb7e63a9a5..0474840224d9 100644 --- a/arch/arm/mm/dma-mapping.c +++ b/arch/arm/mm/dma-mapping.c @@ -719,8 +719,10 @@ static void __dma_page_dev_to_cpu(struct page *page, unsigned long off, } while (left >= (ssize_t)folio_size(folio)) { - set_bit(PG_dcache_clean, &folio->flags); left -= folio_size(folio); + set_bit(PG_dcache_clean, &folio->flags); + if (!left) + break; folio = folio_next(folio); } } -- 2.34.1
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