netdev - Re: possible memory leak in ipc

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Date:   Fri, 26 Aug 2016 10:27:03 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>, CAI Qian <caiqian@...hat.com>,
        Thomas Graf <tgraf@...g.ch>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: possible memory leak in ipc

On Fri, Aug 26, 2016 at 10:04 AM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> It was correct until...
>
> commit 4cf0b354d92ee2c642532ee39e330f8f580fd985
> Author: Florian Westphal <fw@...len.de>
> Date:   Fri Aug 12 12:03:52 2016 +0200
>
>     rhashtable: avoid large lock-array allocations
>
>
> which is:
>
> @@ -83,6 +83,9 @@ static int alloc_bucket_locks(struct rhashtable *ht,
> struct bucket_table *tbl,
>                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
>                 else
>  #endif
> +               if (gfp != GFP_KERNEL)
> +                       gfp |= __GFP_NOWARN | __GFP_NORETRY;
> +
>                 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
>                                            gfp);

Heh.

Yeah, this is a classic case of something we should *not* do.

And I'm not speaking out against that commit 4cf0b354d92e itself: that
isn't the problem. The problem is that #ifdef with the rather subtle
dangling 'else'. Oops.

I even *looked* at that function yesterday, and didn't realize the (in
hindsight) obvious bug because the code had that odd pattern.

I see that Eric sent a patch and fixed the bug, and in the process got
rid of that dangling else thing.

Thanks guys,

              Linus