linux-kernel - [PATCH] swiotlb: Fix passing local variable to debugfs_create

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Date:   Thu, 28 Jul 2022 03:24:20 -0400
From:   Tianyu Lan <ltykernel@...il.com>
To:     hch@...radead.org, m.szyprowski@...sung.com, robin.murphy@....com
Cc:     Tianyu Lan <tiala@...rosoft.com>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] swiotlb: Fix passing local variable to debugfs_create_ulong()

From: Tianyu Lan <tiala@...rosoft.com>

Debugfs node will be run-timely checked and so local variable
should be not passed to debugfs_create_ulong(). Fix it via
debugfs_create_file() to create io_tlb_used node and calculate
used io tlb number with fops_io_tlb_used attribute.

Fixes: 20347fca71a3 ("swiotlb: split up the global swiotlb lock")
Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
---
 kernel/dma/swiotlb.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index cc50f1fb127f..69986cffda5f 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -912,17 +912,24 @@ bool is_swiotlb_active(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(is_swiotlb_active);
 
+static int io_tlb_used_get(void *data, u64 *val)
+{
+	*val = mem_used(&io_tlb_default_mem);
+
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(fops_io_tlb_used, io_tlb_used_get, NULL, "%llu\n");
+
 static void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,
 					 const char *dirname)
 {
-	unsigned long used = mem_used(mem);
-
 	mem->debugfs = debugfs_create_dir(dirname, io_tlb_default_mem.debugfs);
 	if (!mem->nslabs)
 		return;
 
 	debugfs_create_ulong("io_tlb_nslabs", 0400, mem->debugfs, &mem->nslabs);
-	debugfs_create_ulong("io_tlb_used", 0400, mem->debugfs, &used);
+	debugfs_create_file("io_tlb_used", 0400, mem->debugfs, NULL,
+			&fops_io_tlb_used);
 }
 
 static int __init __maybe_unused swiotlb_create_default_debugfs(void)
-- 
2.25.1