netdev - Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP

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Message-ID: <20220926100800.GB12777@breakpoint.cc>
Date:   Mon, 26 Sep 2022 12:08:00 +0200
From:   Florian Westphal <fw@...len.de>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Florian Westphal <fw@...len.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, vbabka@...e.cz,
        akpm@...ux-foundation.org, urezki@...il.com,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        Martin Zaharinov <micron10@...il.com>
Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC

Michal Hocko <mhocko@...e.com> wrote:
> +		old_tbl = rht_dereference_rcu(ht->tbl, ht);
> +		size = tbl->size;
> +
> +		data = ERR_PTR(-EBUSY);
> +
> +		if (rht_grow_above_75(ht, tbl))
> +			size *= 2;
> +		/* Do not schedule more than one rehash */
> +		else if (old_tbl != tbl)
> +			return data;
> +
> +		data = ERR_PTR(-ENOMEM);
> +
> +		rcu_read_unlock();
> +		new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
> +		rcu_read_lock();

I don't think this is going to work, there can be callers that
rely on rcu protected data structures getting free'd.

Also, network stack assumes synchronize_rcu() means that all
inflight packets have completed processing.