From: Peter Zijlstra <peterz@infradead.org>
To: Xiaoming Ni <nixiaoming@huawei.com>
Cc: paul@paul-moore.com, edumazet@google.com, paulmck@kernel.org,
dhowells@redhat.com, keescook@chromium.org, shakeelb@google.com,
jamorris@linux.microsoft.com, alex.huangjianhui@huawei.com,
dylix.dailei@huawei.com, chenzefeng2@huawei.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC] cred: Add WARN to detect wrong use of get/put_cred
Date: Fri, 12 Jun 2020 18:33:45 +0200 [thread overview]
Message-ID: <20200612163345.GF2497@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1591957695-118312-1-git-send-email-nixiaoming@huawei.com>
On Fri, Jun 12, 2020 at 06:28:15PM +0800, Xiaoming Ni wrote:
> Cred release and usage check code flow:
> 1. put_cred()
> if (atomic_dec_and_test(&(cred)->usage))
> __put_cred(cred);
>
> 2. __put_cred()
> BUG_ON(atomic_read(&cred->usage) != 0);
> call_rcu(&cred->rcu, put_cred_rcu);
>
> 3. put_cred_rcu()
> if (atomic_read(&cred->usage) != 0)
> panic("CRED: put_cred_rcu() sees %p with usage %d\n",
> cred, atomic_read(&cred->usage));
> kmem_cache_free(cred_jar, cred);
>
> If panic is triggered on put_cred_rcu(), there are two possibilities
> 1. Call get_cred() after __put_cred(), usage > 0
> 2. Call put_cred() after __put_cred(), usage < 0
> Since put_cred_rcu is an asynchronous behavior, it is no longer the first
> scene when panic, there is no information about the murderer in the panic
> call stack...
>
> So, add WARN() in get_cred()/put_cred(), and pray to catch the murderer
> at the first scene.
Why not not use refcount_t? It has all that goodness and more.
next prev parent reply other threads:[~2020-06-12 16:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-12 10:28 [PATCH RFC] cred: Add WARN to detect wrong use of get/put_cred Xiaoming Ni
2020-06-12 16:16 ` David Laight
2020-06-12 16:32 ` Eric Dumazet
2020-06-12 16:33 ` Peter Zijlstra [this message]
2020-06-12 17:06 ` Kees Cook
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