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Date:   Tue, 03 Aug 2021 07:39:03 +0000
From:   yajun.deng@...ux.dev
To:     "Jakub Kicinski" <kuba@...nel.org>,
        "David Ahern" <dsahern@...il.com>
Cc:     "Matthieu Baerts" <matthieu.baerts@...sares.net>,
        "David Ahern" <dsahern@...nel.org>, ciorneiioana@...il.com,
        netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net-next] ipv4: Fix refcount warning for new fib_info

August 3, 2021 4:20 AM, "Jakub Kicinski" <kuba@...nel.org> wrote:

> On Mon, 2 Aug 2021 12:04:01 -0600 David Ahern wrote:
> 
>> On 8/2/21 11:58 AM, Matthieu Baerts wrote:
>> Hi David,
>> 
>> On 02/08/2021 18:02, David Ahern wrote:
>> Ioana reported a refcount warning when booting over NFS:
>> 
>> [ 5.042532] ------------[ cut here ]------------
>> [ 5.047184] refcount_t: addition on 0; use-after-free.
>> [ 5.052324] WARNING: CPU: 7 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0xa4/0x150
>> ...
>> [ 5.167201] Call trace:
>> [ 5.169635] refcount_warn_saturate+0xa4/0x150
>> [ 5.174067] fib_create_info+0xc00/0xc90
>> [ 5.177982] fib_table_insert+0x8c/0x620
>> [ 5.181893] fib_magic.isra.0+0x110/0x11c
>> [ 5.185891] fib_add_ifaddr+0xb8/0x190
>> [ 5.189629] fib_inetaddr_event+0x8c/0x140
>> 
>> fib_treeref needs to be set after kzalloc. The old code had a ++ which
>> led to the confusion when the int was replaced by a refcount_t.
>> 
>> Thank you for the patch!
>> 
>> My CI was also complaining of not being able to run kernel selftests [1].
>> Your patch fixes the issue, thanks!
>> 
>> Tested-by: Matthieu Baerts <matthieu.baerts@...sares.net>
>> 
>> Given how easily it is to trigger the warning, I get the impression the
>> original was an untested patch.
> 
> Yeah :( In hindsight any refcount patch which doesn't contain a
> refcount_set() is suspicious. Thanks for the quick fix, applied!

Sorry for that, there is another patch needed to apply for the same reason. I just submitted it.

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