[PATCH 5/9] ipv4: tcp_output: avoid warning about NET_ADD_STATS

Arnd Bergmann
2024-03-28T14:31:53Z

From: Arnd Bergmann <arnd@arndb.de>

Clang warns about a range check in percpu_add_op() being impossible
to hit for an u8 variable:

net/ipv4/tcp_output.c:188:3: error: result of comparison of constant -1 with expression of type 'u8' (aka 'unsigned char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/net/ip.h:291:41: note: expanded from macro 'NET_ADD_STATS'
#define NET_ADD_STATS(net, field, adnd) SNMP_ADD_STATS((net)->mib.net_statistics, field, adnd)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/net/snmp.h:143:4: note: expanded from macro 'SNMP_ADD_STATS'
this_cpu_add(mib->mibs[field], addend)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/percpu-defs.h:509:33: note: expanded from macro 'this_cpu_add'
#define this_cpu_add(pcp, val) __pcpu_size_call(this_cpu_add_, pcp, val)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
<scratch space>:187:1: note: expanded from here
this_cpu_add_8
^
arch/x86/include/asm/percpu.h:326:35: note: expanded from macro 'this_cpu_add_8'
#define this_cpu_add_8(pcp, val) percpu_add_op(8, volatile, (pcp), val)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/x86/include/asm/percpu.h:127:31: note: expanded from macro 'percpu_add_op'
((val) == 1 || (val) == -1)) ? \
~~~~~ ^ ~~

Avoid this warning with a cast to a signed 'int'.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
net/ipv4/tcp_output.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index e3167ad96567..dbe54fceee08 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -183,7 +183,7 @@ static inline void tcp_event_ack_sent(struct sock *sk, u32 rcv_nxt)

if (unlikely(tp->compressed_ack)) {
NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
- tp->compressed_ack);
+ (int)tp->compressed_ack);
tp->compressed_ack = 0;
if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
__sock_put(sk);
--
2.39.2