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    SubjectRe: [PATCH v9 01/10] btf: Add a new kfunc flag which allows to mark a function to be sleepable
    On Tue, Aug 09, 2022 at 03:45:54PM +0200, Roberto Sassu wrote:
    > From: Benjamin Tissoires <benjamin.tissoires@redhat.com>
    >
    > From: Benjamin Tissoires <benjamin.tissoires@redhat.com>
    >
    > This allows to declare a kfunc as sleepable and prevents its use in
    > a non sleepable program.

    Nit: "Declare a kfunc as sleepable and prevent its use in a
    non-sleepable program."

    It's missing the part *how* the patch accomplishes its goals.

    >
    > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
    > Co-developed-by: Yosry Ahmed <yosryahmed@google.com>
    > Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
    > Signed-off-by: Hao Luo <haoluo@google.com>
    > ---
    > Documentation/bpf/kfuncs.rst | 6 ++++++
    > include/linux/btf.h | 1 +
    > kernel/bpf/btf.c | 9 +++++++++
    > 3 files changed, 16 insertions(+)
    >
    > diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
    > index c0b7dae6dbf5..c8b21de1c772 100644
    > --- a/Documentation/bpf/kfuncs.rst
    > +++ b/Documentation/bpf/kfuncs.rst
    > @@ -146,6 +146,12 @@ that operate (change some property, perform some operation) on an object that
    > was obtained using an acquire kfunc. Such kfuncs need an unchanged pointer to
    > ensure the integrity of the operation being performed on the expected object.
    >
    > +2.4.6 KF_SLEEPABLE flag
    > +-----------------------
    > +
    > +The KF_SLEEPABLE flag is used for kfuncs that may sleep. Such kfuncs can only
    > +be called by sleepable BPF programs (BPF_F_SLEEPABLE).
    > +
    > 2.5 Registering the kfuncs
    > --------------------------
    >
    > diff --git a/include/linux/btf.h b/include/linux/btf.h
    > index cdb376d53238..976cbdd2981f 100644
    > --- a/include/linux/btf.h
    > +++ b/include/linux/btf.h
    > @@ -49,6 +49,7 @@
    > * for this case.
    > */
    > #define KF_TRUSTED_ARGS (1 << 4) /* kfunc only takes trusted pointer arguments */
    > +#define KF_SLEEPABLE (1 << 5) /* kfunc may sleep */
    >
    > struct btf;
    > struct btf_member;
    > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
    > index 7e64447659f3..d3e4c86b8fcd 100644
    > --- a/kernel/bpf/btf.c
    > +++ b/kernel/bpf/btf.c
    > @@ -6175,6 +6175,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
    > {
    > enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
    > bool rel = false, kptr_get = false, trusted_arg = false;
    > + bool sleepable = false;
    > struct bpf_verifier_log *log = &env->log;
    > u32 i, nargs, ref_id, ref_obj_id = 0;
    > bool is_kfunc = btf_is_kernel(btf);
    > @@ -6212,6 +6213,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
    > rel = kfunc_flags & KF_RELEASE;
    > kptr_get = kfunc_flags & KF_KPTR_GET;
    > trusted_arg = kfunc_flags & KF_TRUSTED_ARGS;
    > + sleepable = kfunc_flags & KF_SLEEPABLE;
    > }
    >
    > /* check that BTF function arguments match actual types that the
    > @@ -6419,6 +6421,13 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
    > func_name);
    > return -EINVAL;
    > }
    > +
    > + if (sleepable && !env->prog->aux->sleepable) {
    > + bpf_log(log, "kernel function %s is sleepable but the program is not\n",
    > + func_name);
    > + return -EINVAL;
    > + }
    > +
    > /* returns argument register number > 0 in case of reference release kfunc */
    > return rel ? ref_regno : 0;
    > }
    > --
    > 2.25.1
    >

    BR, Jarkko

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