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From: Eric Dumazet <edumazet@google.com>
Date: Fri, 1 Mar 2024 10:09:45 +0100
Message-ID: <CANn89iKpsHTQ9Zqz4cbCGOuj8sp5CCYGHe3Wvk2cyQL4HPADkw@mail.gmail.com>
Subject: Re: linux-next: build failure after merge of the net-next tree
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: David Miller <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, 
	Paolo Abeni <pabeni@redhat.com>, Networking <netdev@vger.kernel.org>, Jiri Pirko <jiri@nvidia.com>, 
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, 
	Linux Next Mailing List <linux-next@vger.kernel.org>
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On Fri, Mar 1, 2024 at 2:11=E2=80=AFAM Stephen Rothwell <sfr@canb.auug.org.=
au> wrote:
>
> Hi all,
>
> After merging the net-next tree, today's linux-next build (arm
> multi_v7_defconfig) failed like this:
>
> In file included from <command-line>:
> In function 'tcp_struct_check',
>     inlined from 'tcp_init' at net/ipv4/tcp.c:4700:2:
> include/linux/compiler_types.h:442:45: error: call to '__compiletime_asse=
rt_940' declared with attribute error: BUILD_BUG_ON failed: offsetof(struct=
 tcp_sock, __cacheline_group_end__tcp_sock_write_rx) - offsetofend(struct t=
cp_sock, __cacheline_group_begin__tcp_sock_write_rx) > 99
>   442 |         _compiletime_assert(condition, msg, __compiletime_assert_=
, __COUNTER__)
>       |                                             ^
> include/linux/compiler_types.h:423:25: note: in definition of macro '__co=
mpiletime_assert'
>   423 |                         prefix ## suffix();                      =
       \
>       |                         ^~~~~~
> include/linux/compiler_types.h:442:9: note: in expansion of macro '_compi=
letime_assert'
>   442 |         _compiletime_assert(condition, msg, __compiletime_assert_=
, __COUNTER__)
>       |         ^~~~~~~~~~~~~~~~~~~
> include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime=
_assert'
>    39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), m=
sg)
>       |                                     ^~~~~~~~~~~~~~~~~~
> include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON=
_MSG'
>    50 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #cond=
ition)
>       |         ^~~~~~~~~~~~~~~~
> include/linux/cache.h:108:9: note: in expansion of macro 'BUILD_BUG_ON'
>   108 |         BUILD_BUG_ON(offsetof(TYPE, __cacheline_group_end__##GROU=
P) - \
>       |         ^~~~~~~~~~~~
> net/ipv4/tcp.c:4687:9: note: in expansion of macro 'CACHELINE_ASSERT_GROU=
P_SIZE'
>  4687 |         CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_wri=
te_rx, 99);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Caused by commit
>
>   99123622050f ("tcp: remove some holes in struct tcp_sock")
>
> I have reverted that commit for today.
>

I have no idea. Maybe this arch has some unusual alignments on
u64/u32/u16 fields ?

The patch should not have changed tcp_sock_write_rx group...

My patch reduced tcp_sock_write_tx on x86_64 from 113 to 105 bytes but
I did not bother changing the assert,
because the assertion triggers if the size of the group is bigger than
the numerical value.

So I could have added the following, but really did not bother.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c82dc42f57c65df112f79080ff407cd98d11ce68..7e1b848398d04f2da2a91c3af97=
b1e2e3895b8ee
100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4651,7 +4651,7 @@ static void __init tcp_struct_check(void)
        CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock,
tcp_sock_write_tx, tsorted_sent_queue);
        CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock,
tcp_sock_write_tx, highest_sack);
        CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock,
tcp_sock_write_tx, ecn_flags);
-       CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_tx, 113=
);
+       CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_tx, 105=
);

        /* TXRX read-write hotpath cache lines */
        CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock,
tcp_sock_write_txrx, pred_flags);