6.6-stable review patch. If anyone has any objections, please let me know.
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From: Peilin Ye yepeilin@google.com
[ Upstream commit 6d78b4473cdb08b74662355a9e8510bde09c511e ]
Currently, calling bpf_map_kmalloc_node() from __bpf_async_init() can cause various locking issues; see the following stack trace (edited for style) as one example:
... [10.011566] do_raw_spin_lock.cold [10.011570] try_to_wake_up (5) double-acquiring the same [10.011575] kick_pool rq_lock, causing a hardlockup [10.011579] __queue_work [10.011582] queue_work_on [10.011585] kernfs_notify [10.011589] cgroup_file_notify [10.011593] try_charge_memcg (4) memcg accounting raises an [10.011597] obj_cgroup_charge_pages MEMCG_MAX event [10.011599] obj_cgroup_charge_account [10.011600] __memcg_slab_post_alloc_hook [10.011603] __kmalloc_node_noprof ... [10.011611] bpf_map_kmalloc_node [10.011612] __bpf_async_init [10.011615] bpf_timer_init (3) BPF calls bpf_timer_init() [10.011617] bpf_prog_xxxxxxxxxxxxxxxx_fcg_runnable [10.011619] bpf__sched_ext_ops_runnable [10.011620] enqueue_task_scx (2) BPF runs with rq_lock held [10.011622] enqueue_task [10.011626] ttwu_do_activate [10.011629] sched_ttwu_pending (1) grabs rq_lock ...
The above was reproduced on bpf-next (b338cf849ec8) by modifying ./tools/sched_ext/scx_flatcg.bpf.c to call bpf_timer_init() during ops.runnable(), and hacking the memcg accounting code a bit to make a bpf_timer_init() call more likely to raise an MEMCG_MAX event.
We have also run into other similar variants (both internally and on bpf-next), including double-acquiring cgroup_file_kn_lock, the same worker_pool::lock, etc.
As suggested by Shakeel, fix this by using __GFP_HIGH instead of GFP_ATOMIC in __bpf_async_init(), so that e.g. if try_charge_memcg() raises an MEMCG_MAX event, we call __memcg_memory_event() with @allow_spinning=false and avoid calling cgroup_file_notify() there.
Depends on mm patch "memcg: skip cgroup_file_notify if spinning is not allowed": https://lore.kernel.org/bpf/20250905201606.66198-1-shakeel.butt@linux.dev/
v0 approach s/bpf_map_kmalloc_node/bpf_mem_alloc/ https://lore.kernel.org/bpf/20250905061919.439648-1-yepeilin@google.com/ v1 approach: https://lore.kernel.org/bpf/20250905234547.862249-1-yepeilin@google.com/
Fixes: b00628b1c7d5 ("bpf: Introduce bpf timers.") Suggested-by: Shakeel Butt shakeel.butt@linux.dev Signed-off-by: Peilin Ye yepeilin@google.com Link: https://lore.kernel.org/r/20250909095222.2121438-1-yepeilin@google.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/helpers.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 4b20a72ab8cff..90c281e1379ee 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -1204,8 +1204,11 @@ static int __bpf_async_init(struct bpf_async_kern *async, struct bpf_map *map, u goto out; }
- /* allocate hrtimer via map_kmalloc to use memcg accounting */ - cb = bpf_map_kmalloc_node(map, size, GFP_ATOMIC, map->numa_node); + /* Allocate via bpf_map_kmalloc_node() for memcg accounting. Until + * kmalloc_nolock() is available, avoid locking issues by using + * __GFP_HIGH (GFP_ATOMIC & ~__GFP_RECLAIM). + */ + cb = bpf_map_kmalloc_node(map, size, __GFP_HIGH, map->numa_node); if (!cb) { ret = -ENOMEM; goto out;