linux-kernel - [PATCH] arm: dma-mapping: fix potential endless loop in __dma_page_dev_to

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Message-Id: <20230807152657.1692414-1-m.szyprowski@samsung.com>
Date:   Mon,  7 Aug 2023 17:26:57 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Russell King <linux@...linux.org.uk>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: [PATCH] arm: dma-mapping: fix potential endless loop in
 __dma_page_dev_to_cpu()

It is possible that the folio_size() of the next folio returns zero, so
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
 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---

Fixes: cc24e9c0895c ("arm: implement the new page table range API")
Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
---
 arch/arm/mm/dma-mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 70cb7e63a9a5..02250106e5ed 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -718,7 +718,7 @@ static void __dma_page_dev_to_cpu(struct page *page, unsigned long off,
 			folio = folio_next(folio);
 		}
 
-		while (left >= (ssize_t)folio_size(folio)) {
+		while (left && left >= (ssize_t)folio_size(folio)) {
 			set_bit(PG_dcache_clean, &folio->flags);
 			left -= folio_size(folio);
 			folio = folio_next(folio);
-- 
2.34.1