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

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Date:   Mon, 26 Sep 2022 16:05:45 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Florian Westphal <fw@...len.de>
Cc:     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

On Mon 26-09-22 15:08:08, Florian Westphal wrote:
[...]
> To the best of my knowledge there are users of this interface that
> invoke it with rcu read lock held, and since those always nest, the
> rcu_read_unlock() won't move us to GFP_KERNEL territory.

Fiar point. I can see a comment above rhashtable_insert_fast which is
supposed to be used by drivers and explicitly documented to be
compatible with an atomic context. So the above is clearly a no-go

In that case I would propose to go with the patch going
http://lkml.kernel.org/r/YzFplwSxwwsLpzzX@dhcp22.suse.cz direction.
For that we could use an alternative implementation for the vmalloc
fallback for non-sleeping request in the future. A single branch for an
unlikely event is not nice but acceptable I would say. Especially if we
want to go in line with Linus' original "prevent hack for gfp_mask in
callers".
-- 
Michal Hocko
SUSE Labs