On Wed, Nov 4, 2020 at 3:26 AM David Verbeiren
<david.verbeiren@xxxxxxxxxxxx> wrote:
>
> Zero-fill element values for all other cpus than current, just as
> when not using prealloc. This is the only way the bpf program can
> ensure known initial values for all cpus ('onallcpus' cannot be
> set when coming from the bpf program).
>
> The scenario is: bpf program inserts some elements in a per-cpu
> map, then deletes some (or userspace does). When later adding
> new elements using bpf_map_update_elem(), the bpf program can
> only set the value of the new elements for the current cpu.
> When prealloc is enabled, previously deleted elements are re-used.
> Without the fix, values for other cpus remain whatever they were
> when the re-used entry was previously freed.
>
> A selftest is added to validate correct operation in above
> scenario as well as in case of LRU per-cpu map element re-use.
>
> Fixes: 6c9059817432 ("bpf: pre-allocate hash map elements")
> Acked-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx>
> Signed-off-by: David Verbeiren <david.verbeiren@xxxxxxxxxxxx>
> ---
>
> Notes:
> v4:
> - Replaced racy "once" test by getpgid syscall with
> check on pid. (Andrii)
> - Copyright lines use /* */ (Andrii)
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
>
> v3:
> - Added selftest that was initially provided as separate
> patch, and reworked to
> * use skeleton (Andrii, Song Liu)
> * skip test if <=1 CPU (Song Liu)
>
> v2:
> - Moved memset() to separate pcpu_init_value() function,
> which replaces pcpu_copy_value() but delegates to it
> for the cases where no memset() is needed (Andrii).
> - This function now also avoids doing the memset() for
> the current cpu for which the value must be set
> anyhow (Andrii).
> - Same pcpu_init_value() used for per-cpu LRU map
> (Andrii).
>
> kernel/bpf/hashtab.c | 30 ++-
> .../selftests/bpf/prog_tests/map_init.c | 214 ++++++++++++++++++
> .../selftests/bpf/progs/test_map_init.c | 33 +++
> 3 files changed, 275 insertions(+), 2 deletions(-)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/map_init.c
> create mode 100644 tools/testing/selftests/bpf/progs/test_map_init.c
>
[...]
