Messages in this thread | | | Subject | Re: [PATCH bpf-next 1/4] bpf: enable task local storage for tracing programs | From | Yonghong Song <> | Date | Tue, 12 Jan 2021 08:32:18 -0800 |
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On 1/11/21 3:45 PM, Song Liu wrote: > > >> On Jan 11, 2021, at 1:58 PM, Martin Lau <kafai@fb.com> wrote: >> >> On Mon, Jan 11, 2021 at 10:35:43PM +0100, KP Singh wrote: >>> On Mon, Jan 11, 2021 at 7:57 PM Martin KaFai Lau <kafai@fb.com> wrote: >>>> >>>> On Fri, Jan 08, 2021 at 03:19:47PM -0800, Song Liu wrote: >>>> >>>> [ ... ] >>>> >>>>> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c >>>>> index dd5aedee99e73..9bd47ad2b26f1 100644 >>>>> --- a/kernel/bpf/bpf_local_storage.c >>>>> +++ b/kernel/bpf/bpf_local_storage.c >>>>> @@ -140,17 +140,18 @@ static void __bpf_selem_unlink_storage(struct bpf_local_storage_elem *selem) >>>>> { >>>>> struct bpf_local_storage *local_storage; >>>>> bool free_local_storage = false; >>>>> + unsigned long flags; >>>>> >>>>> if (unlikely(!selem_linked_to_storage(selem))) >>>>> /* selem has already been unlinked from sk */ >>>>> return; >>>>> >>>>> local_storage = rcu_dereference(selem->local_storage); >>>>> - raw_spin_lock_bh(&local_storage->lock); >>>>> + raw_spin_lock_irqsave(&local_storage->lock, flags); >>>> It will be useful to have a few words in commit message on this change >>>> for future reference purpose. >>>> >>>> Please also remove the in_irq() check from bpf_sk_storage.c >>>> to avoid confusion in the future. It probably should >>>> be in a separate patch. >>>> >>>> [ ... ] >>>> >>>>> diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c >>>>> index 4ef1959a78f27..f654b56907b69 100644 >>>>> diff --git a/kernel/fork.c b/kernel/fork.c >>>>> index 7425b3224891d..3d65c8ebfd594 100644 >>>> [ ... ] >>>> >>>>> --- a/kernel/fork.c >>>>> +++ b/kernel/fork.c >>>>> @@ -96,6 +96,7 @@ >>>>> #include <linux/kasan.h> >>>>> #include <linux/scs.h> >>>>> #include <linux/io_uring.h> >>>>> +#include <linux/bpf.h> >>>>> >>>>> #include <asm/pgalloc.h> >>>>> #include <linux/uaccess.h> >>>>> @@ -734,6 +735,7 @@ void __put_task_struct(struct task_struct *tsk) >>>>> cgroup_free(tsk); >>>>> task_numa_free(tsk, true); >>>>> security_task_free(tsk); >>>>> + bpf_task_storage_free(tsk); >>>>> exit_creds(tsk); >>>> If exit_creds() is traced by a bpf and this bpf is doing >>>> bpf_task_storage_get(..., BPF_LOCAL_STORAGE_GET_F_CREATE), >>>> new task storage will be created after bpf_task_storage_free(). >>>> >>>> I recalled there was an earlier discussion with KP and KP mentioned >>>> BPF_LSM will not be called with a task that is going away. >>>> It seems enabling bpf task storage in bpf tracing will break >>>> this assumption and needs to be addressed? >>> >>> For tracing programs, I think we will need an allow list where >>> task local storage can be used. >> Instead of whitelist, can refcount_inc_not_zero(&tsk->usage) be used? > > I think we can put refcount_inc_not_zero() in bpf_task_storage_get, like: > > diff --git i/kernel/bpf/bpf_task_storage.c w/kernel/bpf/bpf_task_storage.c > index f654b56907b69..93d01b0a010e6 100644 > --- i/kernel/bpf/bpf_task_storage.c > +++ w/kernel/bpf/bpf_task_storage.c > @@ -216,6 +216,9 @@ BPF_CALL_4(bpf_task_storage_get, struct bpf_map *, map, struct task_struct *, > * by an RCU read-side critical section. > */ > if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) { > + if (!refcount_inc_not_zero(&task->usage)) > + return -EBUSY; > + > sdata = bpf_local_storage_update( > task, (struct bpf_local_storage_map *)map, value, > BPF_NOEXIST); > > But where shall we add the refcount_dec()? IIUC, we cannot add it to > __put_task_struct().
Maybe put_task_struct()?
> Thanks, > Song >
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