From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: David Verbeiren <david.verbeiren@tessares.net>
Cc: bpf <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
Networking <netdev@vger.kernel.org>,
Matthieu Baerts <matthieu.baerts@tessares.net>
Subject: Re: [PATCH bpf v4] bpf: zero-fill re-used per-cpu map element
Date: Wed, 4 Nov 2020 12:45:50 -0800 [thread overview]
Message-ID: <CAEf4BzaK4Lbac=A8dsRyCLCbdwTbXEJFXFU113kYv1UVCV9TyQ@mail.gmail.com> (raw)
In-Reply-To: <20201104112332.15191-1-david.verbeiren@tessares.net>
On Wed, Nov 4, 2020 at 3:26 AM David Verbeiren
<david.verbeiren@tessares.net> 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@tessares.net>
> Signed-off-by: David Verbeiren <david.verbeiren@tessares.net>
> ---
>
> Notes:
> v4:
> - Replaced racy "once" test by getpgid syscall with
> check on pid. (Andrii)
> - Copyright lines use /* */ (Andrii)
Acked-by: Andrii Nakryiko <andrii@kernel.org>
>
> 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
>
[...]
next prev parent reply other threads:[~2020-11-04 20:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 12:37 [PATCH bpf] bpf: zero-fill re-used per-cpu map element David Verbeiren
2020-10-26 22:47 ` Andrii Nakryiko
2020-10-27 14:48 ` David Verbeiren
2020-10-27 22:13 ` [PATCH bpf v2] " David Verbeiren
2020-10-27 22:55 ` Andrii Nakryiko
2020-10-29 14:44 ` David Verbeiren
2020-10-29 22:40 ` Andrii Nakryiko
2020-11-03 15:47 ` [PATCH bpf v3] " David Verbeiren
2020-11-03 18:19 ` Andrii Nakryiko
2020-11-04 11:23 ` [PATCH bpf v4] " David Verbeiren
2020-11-04 20:45 ` Andrii Nakryiko [this message]
2020-11-06 4:10 ` patchwork-bot+netdevbpf
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