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From:   Eric Dumazet <edumazet@google.com>
Date:   Wed, 8 Sep 2021 07:50:13 -0700
Message-ID: <CANn89iJzyPbR-fS8S_oAMSJzUGTHAfx49CXVc6ZSckUk91Opvg@mail.gmail.com>
Subject: Re: ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger
 than 1024 bytes [-Werror=frame-larger-than=]
To:     Thorsten Glaser <t.glaser@tarent.de>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Brendan Higgins <brendanhiggins@google.com>,
        Ariel Elior <aelior@marvell.com>,
        GR-everest-linux-l2@marvell.com, Wei Liu <wei.liu@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        open list <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>, lkft-triage@lists.linaro.org,
        Arnd Bergmann <arnd@arndb.de>,
        "David S. Miller" <davem@davemloft.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>
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On Wed, Sep 8, 2021 at 6:48 AM Thorsten Glaser <t.glaser@tarent.de> wrote:
>
> On Tue, 7 Sep 2021, Linus Torvalds wrote:
>
> > The do_tcp_getsockopt() one in tpc.c is a classic case of "lots of
> > different case statements, many of them with their own struct
> > allocations on stack, and all of them disjoint".
>
> Any compiler developers here? AFAIK the compiler knows the lifetime
> of function-local variables, so why not alias the actual memory
> locations and ranges to minimise stack usage?
>

At least on my builds,  do_tcp_getsockopt() uses less than 512 bytes of stack.

Probably because tcp_zerocopy_receive() is _not_ inlined, by pure luck
I suppose.

Perhaps we should use noinline_for_stack here.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e8b48df73c852a48e51754ea98b1e08bf024bb9e..437910c096b202420518c9e5e5cd26b2194d8aa2
100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2054,9 +2054,10 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
 }

 #define TCP_ZEROCOPY_PAGE_BATCH_SIZE 32
-static int tcp_zerocopy_receive(struct sock *sk,
-                               struct tcp_zerocopy_receive *zc,
-                               struct scm_timestamping_internal *tss)
+static noinline_for_stack int
+tcp_zerocopy_receive(struct sock *sk,
+                    struct tcp_zerocopy_receive *zc,
+                    struct scm_timestamping_internal *tss)
 {
        u32 length = 0, offset, vma_len, avail_len, copylen = 0;
        unsigned long address = (unsigned long)zc->address;