| Message ID | 20200208154209.1797988-11-jolsa@kernel.org |
|---|---|
| State | Superseded |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf: Add trampoline and dispatcher to /proc/kallsyms | expand |
On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <jolsa@kernel.org> wrote: > > When bpf_prog is removed from kallsyms it's on the way > out to be removed, so we don't care about lnode state. > > However the bpf_ksym_del will be used also by bpf_trampoline > and bpf_dispatcher objects, which stay allocated even when > they are not in kallsyms list, hence the lnode re-init. > > The list_del_rcu commentary states that we need to call > synchronize_rcu, before we can change/re-init the list_head > pointers. > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > --- Wouldn't it make more sense to have patches 7 though 10 as a one patch? It's a generalization of ksym from being bpf_prog-specific to be more general (which this initialization fix is part of, arguably). > kernel/bpf/core.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > index 73242fd07893..66b17bea286e 100644 > --- a/kernel/bpf/core.c > +++ b/kernel/bpf/core.c > @@ -676,6 +676,13 @@ void bpf_ksym_del(struct bpf_ksym *ksym) > spin_lock_bh(&bpf_lock); > __bpf_ksym_del(ksym); > spin_unlock_bh(&bpf_lock); > + > + /* > + * As explained in list_del_rcu, We must call synchronize_rcu > + * before changing list_head pointers. > + */ > + synchronize_rcu(); > + INIT_LIST_HEAD_RCU(&ksym->lnode); > } > > static bool bpf_prog_kallsyms_candidate(const struct bpf_prog *fp) > -- > 2.24.1 >
On Tue, Feb 11, 2020 at 10:28:50AM -0800, Andrii Nakryiko wrote: > On Sat, Feb 8, 2020 at 7:43 AM Jiri Olsa <jolsa@kernel.org> wrote: > > > > When bpf_prog is removed from kallsyms it's on the way > > out to be removed, so we don't care about lnode state. > > > > However the bpf_ksym_del will be used also by bpf_trampoline > > and bpf_dispatcher objects, which stay allocated even when > > they are not in kallsyms list, hence the lnode re-init. > > > > The list_del_rcu commentary states that we need to call > > synchronize_rcu, before we can change/re-init the list_head > > pointers. > > > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > > --- > > Wouldn't it make more sense to have patches 7 though 10 as a one > patch? It's a generalization of ksym from being bpf_prog-specific to > be more general (which this initialization fix is part of, arguably). it was my initial change ;-) but then I realized I have to explain several things in the changelog, and that's usually the sign that you need to split the patch.. also I think now it's easier for review and backporting so I prefer it split like this, but if you guys want to squash it together, I'll do it ;-) jirka > > > kernel/bpf/core.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > > index 73242fd07893..66b17bea286e 100644 > > --- a/kernel/bpf/core.c > > +++ b/kernel/bpf/core.c > > @@ -676,6 +676,13 @@ void bpf_ksym_del(struct bpf_ksym *ksym) > > spin_lock_bh(&bpf_lock); > > __bpf_ksym_del(ksym); > > spin_unlock_bh(&bpf_lock); > > + > > + /* > > + * As explained in list_del_rcu, We must call synchronize_rcu > > + * before changing list_head pointers. > > + */ > > + synchronize_rcu(); > > + INIT_LIST_HEAD_RCU(&ksym->lnode); > > } > > > > static bool bpf_prog_kallsyms_candidate(const struct bpf_prog *fp) > > -- > > 2.24.1 > > >
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 73242fd07893..66b17bea286e 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -676,6 +676,13 @@ void bpf_ksym_del(struct bpf_ksym *ksym) spin_lock_bh(&bpf_lock); __bpf_ksym_del(ksym); spin_unlock_bh(&bpf_lock); + + /* + * As explained in list_del_rcu, We must call synchronize_rcu + * before changing list_head pointers. + */ + synchronize_rcu(); + INIT_LIST_HEAD_RCU(&ksym->lnode); } static bool bpf_prog_kallsyms_candidate(const struct bpf_prog *fp)
When bpf_prog is removed from kallsyms it's on the way out to be removed, so we don't care about lnode state. However the bpf_ksym_del will be used also by bpf_trampoline and bpf_dispatcher objects, which stay allocated even when they are not in kallsyms list, hence the lnode re-init. The list_del_rcu commentary states that we need to call synchronize_rcu, before we can change/re-init the list_head pointers. Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- kernel/bpf/core.c | 7 +++++++ 1 file changed, 7 insertions(+)