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bpf: Add a recursion check to prevent loops in bpf_timer

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Do not schedule timer/wq operation on a cpu that is in irq_work
callback that is processing async_cmds queue.
Otherwise the following loop is possible:
bpf_timer_start() -> bpf_async_schedule_op() -> irq_work_queue().
irqrestore -> bpf_async_irq_worker() -> tracepoint -> bpf_timer_start().

Fixes: 1bfbc267ec ("bpf: Enable bpf_timer and bpf_wq in any context")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260204055147.54960-4-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov
2026-02-03 21:51:46 -08:00
committed by Andrii Nakryiko
parent 67ee5ad27d
commit 64873307e8
1 changed files with 16 additions and 0 deletions
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16
kernel/bpf/helpers.c
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@@ -1427,9 +1427,23 @@ static int bpf_async_update_prog_callback(struct bpf_async_cb *cb,
return 0;
}
static DEFINE_PER_CPU(struct bpf_async_cb *, async_cb_running);
static int bpf_async_schedule_op(struct bpf_async_cb *cb, enum bpf_async_op op,
u64 nsec, u32 timer_mode)
{
/*
* Do not schedule another operation on this cpu if it's in irq_work
* callback that is processing async_cmds queue. Otherwise the following
* loop is possible:
* bpf_timer_start() -> bpf_async_schedule_op() -> irq_work_queue().
* irqrestore -> bpf_async_irq_worker() -> tracepoint -> bpf_timer_start().
*/
if (this_cpu_read(async_cb_running) == cb) {
bpf_async_refcount_put(cb);
return -EDEADLK;
}
struct bpf_async_cmd *cmd = kmalloc_nolock(sizeof(*cmd), 0, NUMA_NO_NODE);
if (!cmd) {
@@ -1628,6 +1642,7 @@ static void bpf_async_irq_worker(struct irq_work *work)
return;
list = llist_reverse_order(list);
this_cpu_write(async_cb_running, cb);
llist_for_each_safe(pos, n, list) {
struct bpf_async_cmd *cmd;
@@ -1635,6 +1650,7 @@ static void bpf_async_irq_worker(struct irq_work *work)
bpf_async_process_op(cb, cmd->op, cmd->nsec, cmd->mode);
kfree_nolock(cmd);
}
this_cpu_write(async_cb_running, NULL);
}
static void bpf_async_cancel_and_free(struct bpf_async_kern *async)