linux-kernel - [PATCH] mm: fix kmap

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Date: Mon, 1 Jul 2024 01:45:57 +0000
From: Zhangchun <zhang.chunA@....com>
To: "shaohaojize@....com" <shaohaojize@....com>,
        "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiaoxupo
	<jiaoxupo@....com>, Bailin <berlin@....com>,
        Zhangzhansheng
	<zhang.zhansheng@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>, wangyu
	<wang.yuI@....com>
Subject: [PATCH] mm: fix kmap_high deadlock


From: "zhang.chun" <zhang.chuna@....com>

I work with zhangzhansheng(from h3c) find that some situation may casue deadlock when we use kmap_highand kmap_XXX or kumap_xxx between  differt cores at the same time.kmap_high->map_new_virtual-> flush_all_zero_pkmaps->flush_tlb_kernel_range->on_each_cpu,
On this condition, kmap_high
hold the kmap_lock， wait the other cores ack. But the others may disable irq and wait kmap_lock， this is some deadlock condition.
I think it's necessary to give kmap_lock before call flush_tlb_kernel_range.
Like this:
spin_unlock(&kmap_lock);
flush_tlb_kernel_range(xxx);
spin_lock(&kmap_lock);

Signed-off-by: zhang.chun <zhang.chuna@....com>
---
 mm/highmem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/highmem.c b/mm/highmem.c index bd48ba445dd4..12d20e551579 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -221,7 +221,9 @@ static void flush_all_zero_pkmaps(void)
 need_flush = 1;
 }
 if (need_flush)
+spin_unlock(&kmap_lock);
 flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
+spin_lock(&kmap_lock);
 }

 void __kmap_flush_unused(void)
--
2.34.1

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