bpf: adapt selftests to GCC 16 -Wunused-but-set-variable

2026-01-07T05:04:11Z

GCC 16 has changed the semantics of -Wunused-but-set-variable, as well as introducing new options -Wunused-but-set-variable={0,1,2,3} to adjust the level of support. One of the changes is that GCC now treats 'sum += 1' and 'sum++' as non-usage, whereas clang (and GCC < 16) considers the first as usage and the second as non-usage, which is sort of inconsistent. The GCC 16 -Wunused-but-set-variable=2 option implements the previous semantics of -Wunused-but-set-variable, but since it is a new option, it cannot be used unconditionally for forward-compatibility, just for backwards-compatibility. So this patch adds pragmas to the two self-tests impacted by this, progs/free_timer.c and progs/rcu_read_lock.c, to make gcc to ignore -Wunused-but-set-variable warnings when compiling them with GCC > 15. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=44677#c25 for details on why this regression got introduced in GCC upstream. Signed-off-by: Jose E. Marchesi Cc: david.faust@oracle.com Cc: cupertino.miranda@oracle.com Cc: Eduard Zingerman Cc: Yonghong Song Link: https://lore.kernel.org/r/20260106173650.18191-2-jose.marchesi@oracle.com Signed-off-by: Alexei Starovoitov

selftests/bpf: Add test case for the freeing of bpf_timer

2025-01-20T17:09:02Z

The main purpose of the test is to demonstrate the lock problem for the free of bpf_timer under PREEMPT_RT. When freeing a bpf_timer which is running on other CPU in bpf_timer_cancel_and_free(), hrtimer_cancel() will try to acquire a spin-lock (namely softirq_expiry_lock), however the freeing procedure has already held a raw-spin-lock. The test first creates two threads: one to start timers and the other to free timers. The start-timers thread will start the timer and then wake up the free-timers thread to free these timers when the starts complete. After freeing, the free-timer thread will wake up the start-timer thread to complete the current iteration. A loop of 10 iterations is used. Signed-off-by: Hou Tao Link: https://lore.kernel.org/r/20250117101816.2101857-6-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov

kernel.git/tools/testing/selftests/bpf/progs/free_timer.c, branch master

bpf: adapt selftests to GCC 16 -Wunused-but-set-variable

selftests/bpf: Add test case for the freeing of bpf_timer