Messages in this thread | | | Date | Mon, 7 Aug 2023 17:23:28 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH] arm: dma-mapping: fix potential endless loop in __dma_page_dev_to_cpu() |
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On Mon, Aug 07, 2023 at 05:26:57PM +0200, Marek Szyprowski wrote: > It is possible that the folio_size() of the next folio returns zero, so
What? How can folio_size() return zero?
return PAGE_SIZE << folio_order(folio);
It is a minimum of PAGE_SIZE.
> avoid looping with 'left' equals to zero in D-cache cleaning loop. > > This fixes the following endless loop observed by RCU stall: > --->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
I don't know what you've actually hit here, but the explanation is wrong.
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