On Mon, May 16, 2022 at 4:35 PM Tadeusz Struk tadeusz.struk@linaro.org wrote:
On 5/16/22 16:16, Andrii Nakryiko wrote:
On Fri, May 13, 2022 at 12:08 PM Tadeusz Struk tadeusz.struk@linaro.org wrote:
kernel/bpf/cgroup.c | 64 +++++++++++++++++++++++++++++++++++++++------ 1 file changed, 56 insertions(+), 8 deletions(-)
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 128028efda64..9d3af4d6c055 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -681,6 +681,57 @@ static struct bpf_prog_list *find_detach_entry(struct list_head *progs, return ERR_PTR(-ENOENT); }
+/**
- purge_effective_progs() - After compute_effective_progs fails to alloc new
cgrp->bpf.inactive table we can recover by
recomputing the array in place.
- @cgrp: The cgroup which descendants to traverse
- @link: A link to detach
- @atype: Type of detach operation
- */
+static void purge_effective_progs(struct cgroup *cgrp, struct bpf_prog *prog,
enum cgroup_bpf_attach_type atype)+{
struct cgroup_subsys_state *css;struct bpf_prog_array_item *item;struct bpf_prog *tmp;struct bpf_prog_array *array;int index = 0, index_purge = -1;if (!prog)return;/* recompute effective prog array in place */css_for_each_descendant_pre(css, &cgrp->self) {struct cgroup *desc = container_of(css, struct cgroup, self);array = desc->bpf.effective[atype];../kernel/bpf/cgroup.c:748:23: warning: incorrect type in assignment (different address spaces) ../kernel/bpf/cgroup.c:748:23: expected struct bpf_prog_array *array ../kernel/bpf/cgroup.c:748:23: got struct bpf_prog_array [noderef] __rcu *
you need rcu_dereference here? but also see suggestions below to avoid iterating effective directly (it's ambiguous to search by prog only)
I didn't check it with sparse so I didn't see this warning. Will fix in the next version.
item = &array->items[0];/* Find the index of the prog to purge */while ((tmp = READ_ONCE(item->prog))) {if (tmp == prog) {I think comparing just prog isn't always correct, as the same program can be in effective array multiple times if attached through bpf_link.
Looking at replace_effective_prog() I think we can do a very similar (and tested) approach:
- restore original pl state in __cgroup_bpf_detach (so we can find it
by comparing pl->prog == prog && pl->link == link) 2. use replace_effective_prog's approach to find position of pl in effective array (using this nested for loop over cgroup parents and list_for_each_entry inside) 3. then instead of replacing one prog with another do bpf_prog_array_delete_safe_at ?
I'd feel more comfortable using the same tested overall approach of replace_effective_prog.
Ok, I can try that.
index_purge = index;break;}item++;index++;}/* Check if we found what's needed for removing the prog */if (index_purge == -1 || index_purge == index - 1)continue;the search shouldn't fail, should it?
I wasn't if the prog will be present in all parents so I decided to add this check to make sure it is found.
Looking at replace_effective_prog (it's been a while since I touched this code) it has to be present, otherwise it's a bug
/* Remove the program from the array */WARN_ONCE(bpf_prog_array_delete_safe_at(array, index_purge),"Failed to purge a prog from array at index %d", index_purge);index = 0;index_purge = -1;}+}
- /**
- __cgroup_bpf_detach() - Detach the program or link from a cgroup, and
propagate the change to descendants@@ -723,8 +774,11 @@ static int __cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog, pl->link = NULL;
err = update_effective_progs(cgrp, atype);
if (err)goto cleanup;
if (err) {struct bpf_prog *prog_purge = prog ? prog : link->link.prog;so here we shouldn't forget link, instead pass both link and prog (one of them will have to be NULL) into purge_effective_progs
ok, I will pass in both.
-- Thanks, Tadeusz