From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
open list <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>,
Peter Ziljstra <peterz@infradead.org>
Subject: Re: [PATCH v4 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete]
Date: Mon, 22 Feb 2021 22:21:32 -0800 [thread overview]
Message-ID: <CAEf4BzaZ0ATbJsLoQu_SRUYgzkak9zv61N+T=gijOQ+X=57ErA@mail.gmail.com> (raw)
In-Reply-To: <20210223012014.2087583-3-songliubraving@fb.com>
On Mon, Feb 22, 2021 at 5:23 PM Song Liu <songliubraving@fb.com> wrote:
>
> BPF helpers bpf_task_storage_[get|delete] could hold two locks:
> bpf_local_storage_map_bucket->lock and bpf_local_storage->lock. Calling
> these helpers from fentry/fexit programs on functions in bpf_*_storage.c
> may cause deadlock on either locks.
>
> Prevent such deadlock with a per cpu counter, bpf_task_storage_busy, which
> is similar to bpf_prog_active. We need this counter to be global, because
> the two locks here belong to two different objects: bpf_local_storage_map
> and bpf_local_storage. If we pick one of them as the owner of the counter,
> it is still possible to trigger deadlock on the other lock. For example,
> if bpf_local_storage_map owns the counters, it cannot prevent deadlock
> on bpf_local_storage->lock when two maps are used.
>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> kernel/bpf/bpf_task_storage.c | 57 ++++++++++++++++++++++++++++++-----
> 1 file changed, 50 insertions(+), 7 deletions(-)
>
[...]
> @@ -109,7 +136,9 @@ static void *bpf_pid_task_storage_lookup_elem(struct bpf_map *map, void *key)
> goto out;
> }
>
> + bpf_task_storage_lock();
> sdata = task_storage_lookup(task, map, true);
> + bpf_task_storage_unlock();
> put_pid(pid);
> return sdata ? sdata->data : NULL;
> out:
> @@ -141,8 +170,10 @@ static int bpf_pid_task_storage_update_elem(struct bpf_map *map, void *key,
> goto out;
> }
>
> + bpf_task_storage_lock();
> sdata = bpf_local_storage_update(
> task, (struct bpf_local_storage_map *)map, value, map_flags);
this should probably be container_of() instead of casting
> + bpf_task_storage_unlock();
>
> err = PTR_ERR_OR_ZERO(sdata);
> out:
> @@ -185,7 +216,9 @@ static int bpf_pid_task_storage_delete_elem(struct bpf_map *map, void *key)
> goto out;
> }
>
> + bpf_task_storage_lock();
> err = task_storage_delete(task, map);
> + bpf_task_storage_unlock();
> out:
> put_pid(pid);
> return err;
[...]
next prev parent reply other threads:[~2021-02-23 6:24 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 1:20 [PATCH v4 bpf-next 0/6] bpf: enable task local storage for tracing programs Song Liu
2021-02-23 1:20 ` [PATCH v4 bpf-next 1/6] " Song Liu
2021-02-23 3:08 ` kernel test robot
2021-02-23 4:04 ` kernel test robot
2021-02-23 19:23 ` Martin KaFai Lau
2021-02-23 20:51 ` Song Liu
2021-02-23 1:20 ` [PATCH v4 bpf-next 2/6] bpf: prevent deadlock from recursive bpf_task_storage_[get|delete] Song Liu
2021-02-23 6:21 ` Andrii Nakryiko [this message]
2021-02-23 7:16 ` Song Liu
2021-02-23 7:19 ` Andrii Nakryiko
2021-02-23 16:44 ` Alexei Starovoitov
2021-02-23 11:06 ` Peter Zijlstra
2021-02-23 20:49 ` Song Liu
2021-02-23 1:20 ` [PATCH v4 bpf-next 3/6] selftests/bpf: add non-BPF_LSM test for task local storage Song Liu
2021-02-23 1:20 ` [PATCH v4 bpf-next 4/6] selftests/bpf: test deadlock from recursive bpf_task_storage_[get|delete] Song Liu
2021-02-23 1:20 ` [PATCH v4 bpf-next 5/6] bpf: runqslower: prefer using local vmlimux to generate vmlinux.h Song Liu
2021-02-23 6:26 ` Andrii Nakryiko
2021-02-23 21:24 ` Martin KaFai Lau
2021-02-23 1:20 ` [PATCH v4 bpf-next 6/6] bpf: runqslower: use task local storage Song Liu
2021-02-23 21:33 ` Martin KaFai Lau
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