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2d3a1e3615
Currently, if bpf_get_current_cgroup_id() or
bpf_get_current_ancestor_cgroup_id() helper is
called with sleepable programs e.g., sleepable
fentry/fmod_ret/fexit/lsm programs, a rcu warning
may appear. For example, if I added the following
hack to test_progs/test_lsm sleepable fentry program
test_sys_setdomainname:
--- a/tools/testing/selftests/bpf/progs/lsm.c
+++ b/tools/testing/selftests/bpf/progs/lsm.c
@@ -168,6 +168,10 @@ int BPF_PROG(test_sys_setdomainname, struct pt_regs *regs)
int buf = 0;
long ret;
+ __u64 cg_id = bpf_get_current_cgroup_id();
+ if (cg_id == 1000)
+ copy_test++;
+
ret = bpf_copy_from_user(&buf, sizeof(buf), ptr);
if (len == -2 && ret == 0 && buf == 1234)
copy_test++;
I will hit the following rcu warning:
include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
1 lock held by test_progs/260:
#0: ffffffffa5173360 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x0/0xa0
stack backtrace:
CPU: 1 PID: 260 Comm: test_progs Tainted: G O 5.14.0-rc2+ #176
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
Call Trace:
dump_stack_lvl+0x56/0x7b
bpf_get_current_cgroup_id+0x9c/0xb1
bpf_prog_a29888d1c6706e09_test_sys_setdomainname+0x3e/0x89c
bpf_trampoline_6442469132_0+0x2d/0x1000
__x64_sys_setdomainname+0x5/0x110
do_syscall_64+0x3a/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae
I can get similar warning using bpf_get_current_ancestor_cgroup_id() helper.
syzbot reported a similar issue in [1] for syscall program. Helper
bpf_get_current_cgroup_id() or bpf_get_current_ancestor_cgroup_id()
has the following callchain:
task_dfl_cgroup
task_css_set
task_css_set_check
and we have
#define task_css_set_check(task, __c) \
rcu_dereference_check((task)->cgroups, \
lockdep_is_held(&cgroup_mutex) || \
lockdep_is_held(&css_set_lock) || \
((task)->flags & PF_EXITING) || (__c))
Since cgroup_mutex/css_set_lock is not held and the task
is not existing and rcu read_lock is not held, a warning
will be issued. Note that bpf sleepable program is protected by
rcu_read_lock_trace().
The above sleepable bpf programs are already protected
by migrate_disable(). Adding rcu_read_lock() in these
two helpers will silence the above warning.
I marked the patch fixing
|
||
|---|---|---|
| .. | ||
| preload | ||
| arraymap.c | ||
| bpf_inode_storage.c | ||
| bpf_iter.c | ||
| bpf_local_storage.c | ||
| bpf_lru_list.c | ||
| bpf_lru_list.h | ||
| bpf_lsm.c | ||
| bpf_struct_ops_types.h | ||
| bpf_struct_ops.c | ||
| bpf_task_storage.c | ||
| btf.c | ||
| cgroup.c | ||
| core.c | ||
| cpumap.c | ||
| devmap.c | ||
| disasm.c | ||
| disasm.h | ||
| dispatcher.c | ||
| hashtab.c | ||
| helpers.c | ||
| inode.c | ||
| Kconfig | ||
| local_storage.c | ||
| lpm_trie.c | ||
| Makefile | ||
| map_in_map.c | ||
| map_in_map.h | ||
| map_iter.c | ||
| net_namespace.c | ||
| offload.c | ||
| percpu_freelist.c | ||
| percpu_freelist.h | ||
| prog_iter.c | ||
| queue_stack_maps.c | ||
| reuseport_array.c | ||
| ringbuf.c | ||
| stackmap.c | ||
| syscall.c | ||
| sysfs_btf.c | ||
| task_iter.c | ||
| tnum.c | ||
| trampoline.c | ||
| verifier.c | ||