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: <YqANP1K/6oRNCUKZ@google.com>
Date:   Wed, 8 Jun 2022 11:45:19 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        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>
Subject: Re: qemu-arm: zram: mkfs.ext4 : Unable to handle kernel NULL pointer
 dereference at virtual address 00000140

On (22/06/08 11:42), Sergey Senozhatsky wrote:
> > This looks like a NULL lock->name dereference in lockdep. I suspect
> > that somehow local_lock doesn't get .dep_map initialized. Maybe running
> > the kernel with CONFIG_DEBUG_LOCK_ALLOC would help us? Naresh, can you
> > help us with this?
> 
> Hmm, actually, hold on. mapping_area is per-CPU, so what happens if CPU
> get offlined and onlined again? I don't see us re-initializing mapping_area
> local_lock_init(&zs_map_area.lock) and so on.

Something like this?

---

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 9152fbde33b5..ea434a5226a3 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1104,6 +1104,8 @@ static struct zspage *find_get_zspage(struct size_class *class)
 
 static inline int __zs_cpu_up(struct mapping_area *area)
 {
+	local_lock_init(&area->lock);
+
 	/*
 	 * Make sure we don't leak memory if a cpu UP notification
 	 * and zs_init() race and both call zs_cpu_up() on the same cpu