On 3/26/26 5:06 AM, [email protected] wrote: > From: Qingshuang Fu <[email protected]> > > The broadcast_pmtu.sh test verifies that broadcast route MTU is respected, > but it uses an incorrect criteria for test success: it relies solely on > the ping command's exit code, which leads to false failures. > > When the kernel correctly blocks oversized broadcast packets due to the > configured MTU limit (1500), ping fails to transmit any packets and returns > exit code 1. The original script interprets this as a test failure, even > though the kernel is properly enforcing the MTU (the core goal of the test). > > Fix this by: > 1. Checking ping's output for clear signs of MTU enforcement (instead of exit > code) > - Match "0 packets transmitted" (no packets sent due to MTU limit) > - Match "message too long" (kernel rejects oversized packets) > 2. Use an exit code variable to avoid early exit breaking the script flow > 3. Maintain full compatibility with the original setup/cleanup logic > > After this fix, the script returns 0 (success) when the kernel enforces the > broadcast route MTU (packets blocked), and 1 (failure) only when the kernel > fails to enforce the MTU (packets are transmitted but no response is > received). > > Signed-off-by: Qingshuang Fu <[email protected]> > --- > tools/testing/selftests/net/broadcast_pmtu.sh | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/net/broadcast_pmtu.sh > b/tools/testing/selftests/net/broadcast_pmtu.sh > index 726eb5d25839..a8d2a205c51d 100755 > --- a/tools/testing/selftests/net/broadcast_pmtu.sh > +++ b/tools/testing/selftests/net/broadcast_pmtu.sh > @@ -41,7 +41,13 @@ trap cleanup EXIT > > setup && > echo "Testing for broadcast route MTU" && > - ip net exec "${CLIENT_NS}" ping -f -M want -q -c 1 -s 8000 -w 1 -b > "${CLIENT_BROADCAST_ADDRESS}" > /dev/null 2>&1 > - > -exit $? > + ping_output=$(ip net exec "${CLIENT_NS}" ping -f -M want -c 1 -s 8000 > -w 1 -b \ > + "${CLIENT_BROADCAST_ADDRESS}" 2>&1) && > + if echo "${ping_output}" | grep -q -E "0 packets transmitted|message > too long"; then > + exit_code=0 > + else > + exit_code=1 > + fi > + > +exit ${exit_code}
Apparently now the CI test is consistently failing: # selftests: net: broadcast_pmtu.sh # 0.03 [+0.03] Testing for broadcast route MTU not ok 1 selftests: net: broadcast_pmtu.sh # exit=1 /P
