linux-kernel - Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer dereference at virtual address 00000140

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Message-ID: <YqBRZcsfrRMZXMCC@google.com>
Date:   Wed, 8 Jun 2022 16:36:05 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Minchan Kim <minchan@...nel.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        regressions@...ts.linux.dev, Jens Axboe <axboe@...nel.dk>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer
 dereference at virtual address 00000140

On (22/06/08 11:45), Sergey Senozhatsky wrote:
> 
> Something like this?

May be even something like below. Move static initializer to cpu up
hook.

---
 mm/zsmalloc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 9152fbde33b5..6d3789d834e2 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -453,9 +453,7 @@ MODULE_ALIAS("zpool-zsmalloc");
 #endif /* CONFIG_ZPOOL */
 
 /* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
-static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = {
-	.lock	= INIT_LOCAL_LOCK(lock),
-};
+static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
 
 static __maybe_unused int is_first_page(struct page *page)
 {
@@ -1113,6 +1111,7 @@ static inline int __zs_cpu_up(struct mapping_area *area)
 	area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE, GFP_KERNEL);
 	if (!area->vm_buf)
 		return -ENOMEM;
+	local_lock_init(&area->lock);
 	return 0;
 }
 
-- 
2.36.1.255.ge46751e96f-goog