linux-kernel - Re: [PATCH 2/2] rcu: Dump vmalloc memory info safely

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Date:   Sat, 2 Sep 2023 18:28:28 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Zqiang <qiang.zhang1211@...il.com>,
        Zhen Lei <thunder.leizhen@...weicloud.com>,
        "Paul E . McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 2/2] rcu: Dump vmalloc memory info safely

On Wed, 30 Aug 2023 11:04:00 +0000 "Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:

> Currently, for double invoke call_rcu(), will dump rcu_head objects
> memory info, if the objects is not allocated from the slab allocator,
> the vmalloc_dump_obj() will be invoke and the vmap_area_lock spinlock
> need to be held, since the call_rcu() can be invoked in interrupt context,
> therefore, there is a possibility of spinlock deadlock scenarios.
> 
> And in Preempt-RT kernel, the rcutorture test also trigger the following
> lockdep warning:

"possibility of deadlock" sounds like something -stable kernels would
like to have fixed.

Did you consider the desirability of a -stable backport?

If so, are we able to identify a suitable Fixes: target?