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Date:   Mon, 26 Sep 2022 14:02:17 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Florian Westphal <fw@strlen.de>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org, vbabka@suse.cz,
        akpm@linux-foundation.org, urezki@gmail.com,
        netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
        Martin Zaharinov <micron10@gmail.com>
Subject: Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC
Message-ID: <YzGUyWlYd15uLu7G@dhcp22.suse.cz>
References: <20220923103858.26729-1-fw@strlen.de>
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 <20220923133512.GE22541@breakpoint.cc>
 <YzFZf0Onm6/UH7/I@dhcp22.suse.cz>
 <20220926075639.GA908@breakpoint.cc>
 <YzFplwSxwwsLpzzX@dhcp22.suse.cz>
 <YzFxHlYoncuDl2fM@dhcp22.suse.cz>
 <20220926100800.GB12777@breakpoint.cc>
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On Mon 26-09-22 12:08:00, Florian Westphal wrote:
> Michal Hocko <mhocko@suse.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.

The caller of this function drops RCU for each retry, why should be the
called function any special?
-- 
Michal Hocko
SUSE Labs