linux.git/tools/testing/selftests/bpf/progs/rhash_timer.c, branch master Linux kernel source tree selftests/bpf: Test timer field on recycled rhtab element 2026-09-04T19:24:24+00:00 Kumar Kartikeya Dwivedi memxor@gmail.com 2026-09-04T10:41:53+00:00 dbf6806dc81553edbab72fcec9a6d637dedff2f4 Exercise the rhtab special-field lifecycle with the sequence from the original report. A bpf_for_each_map_elem() callback deletes the sole element, then initializes and arms a timer through the callback value pointer while it remains valid. Use a one-element map and pin userspace and BPF execution to one CPU. Repeated delete-and-replace cycles drain the per-CPU allocator cache, and periodic RCU synchronization makes the deleted units available for recycling. After each replacement, a second BPF program calls bpf_timer_cancel() on its value. A successful cancellation proves both that a timer-bearing unit was recycled and that insertion preserved the timer field. Without the fix, insertion clears that field and cancellation keeps returning -EINVAL. A long expiration keeps the timer callback out of the test, so the regression is detected without accessing freed memory. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Link: https://lore.kernel.org/r/20260904104203.345917-3-memxor@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> 
Exercise the rhtab special-field lifecycle with the sequence from the
original report. A bpf_for_each_map_elem() callback deletes the sole
element, then initializes and arms a timer through the callback value
pointer while it remains valid.

Use a one-element map and pin userspace and BPF execution to one CPU.
Repeated delete-and-replace cycles drain the per-CPU allocator cache, and
periodic RCU synchronization makes the deleted units available for
recycling.

After each replacement, a second BPF program calls bpf_timer_cancel()
on its value. A successful cancellation proves both that a timer-bearing
unit was recycled and that insertion preserved the timer field. Without
the fix, insertion clears that field and cancellation keeps returning
-EINVAL. A long expiration keeps the timer callback out of the test, so
the regression is detected without accessing freed memory.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-3-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>