On Tue, Jul 6, 2021 at 3:05 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Tue, Jul 6, 2021 at 11:26 AM Yonghong Song <yhs@xxxxxx> wrote:
> >
> >
> >
> > On 7/6/21 10:44 AM, SanjayKumar J wrote:
> > > task->state is renamed to task->__state in task_struct
> >
> > Could you add a reference to
> > 2f064a59a11f ("sched: Change task_struct::state")
> > which added this change?
> >
> > I think this should go to bpf tree as the change is in linus tree now.
> > Could you annotate the tag as "[PATCH bpf]" ("[PATCH bpf v2]")?
> >
> > Please align comments to the left without margins.
> >
> > >
> > > Signed-off-by: SanjayKumar J <vjsanjay@xxxxxxxxx>
> >
> > This Singed-off-by is not needed.
> >
> > You can add my Ack in the next revision:
> > Acked-by: Yonghong Song <yhs@xxxxxx>
> >
> > >
> > > Signed-off-by: SanjayKumar J <vjsanjay@xxxxxxxxx>
> > > ---
> > > tools/bpf/runqslower/runqslower.bpf.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/bpf/runqslower/runqslower.bpf.c b/tools/bpf/runqslower/runqslower.bpf.c
> > > index 645530ca7e98..ab9353f2fd46 100644
> > > --- a/tools/bpf/runqslower/runqslower.bpf.c
> > > +++ b/tools/bpf/runqslower/runqslower.bpf.c
> > > @@ -74,7 +74,7 @@ int handle__sched_switch(u64 *ctx)
> > > u32 pid;
> > >
> > > /* ivcsw: treat like an enqueue event and store timestamp */
> > > - if (prev->state == TASK_RUNNING)
> > > + if (prev->__state == TASK_RUNNING)
> >
> > Currently, runqslower.bpf.c uses vmlinux.h.
> > I am thinking to use bpf_core_field_exists(), but we need to
> > single out task_struct structure from vmlinux.h
> > with both state and __state fields, we could make it work
> > by *changes* like
> >
> > #define task_struct task_struct_orig
> > #include "vmlinux.h"
> > #undef task_struct
> >
> > struct task_struct {
> > ... state;
> > ... __state;
> > ...
> > };
>
>
> no need for such surgery, recommended way is to use ___suffix to
> declare incompatible struct definition:
>
> struct task_struct___old {
> int state;
> };
>
> Then do casting in BPF code. We don't have to do it in kernel tree's
> runqslower, but we'll definitely have to do that for libbpf-tools'
> runqslower and runqlat.
Question on this topic: state and __state are of different sizes here. IIUC,
bpf_core_types_are_compat() does allow size mismatch. But it may cause
problems in some cases, no? For example, would some combination make
task->state return 32 extra bits from another field and cause confusion?
Thanks,
Song
