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bpf: Use this_cpu_{inc|dec|inc_return} for bpf_task_storage_busy

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Now migrate_disable() does not disable preemption and under some
architectures (e.g. arm64) __this_cpu_{inc|dec|inc_return} are neither
preemption-safe nor IRQ-safe, so for fully preemptible kernel concurrent
lookups or updates on the same task local storage and on the same CPU
may make bpf_task_storage_busy be imbalanced, and
bpf_task_storage_trylock() on the specific cpu will always fail.

Fixing it by using this_cpu_{inc|dec|inc_return} when manipulating
bpf_task_storage_busy.

Fixes: bc235cdb42 ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20220901061938.3789460-2-houtao@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Hou Tao 2022-09-01 14:19:35 +08:00 committed by Martin KaFai Lau
parent c9ae8c966f
commit 197827a05e
2 changed files with 6 additions and 6 deletions
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4
kernel/bpf/bpf_local_storage.c
View file

@ -555,11 +555,11 @@ void bpf_local_storage_map_free(struct bpf_local_storage_map *smap,
struct bpf_local_storage_elem, map_node))) {
if (busy_counter) {
migrate_disable();
__this_cpu_inc(*busy_counter);
this_cpu_inc(*busy_counter);
}
bpf_selem_unlink(selem, false);
if (busy_counter) {
__this_cpu_dec(*busy_counter);
this_cpu_dec(*busy_counter);
migrate_enable();
}
cond_resched_rcu();

8
kernel/bpf/bpf_task_storage.c
View file

@ -26,20 +26,20 @@ static DEFINE_PER_CPU(int, bpf_task_storage_busy);
static void bpf_task_storage_lock(void)
{
migrate_disable();
__this_cpu_inc(bpf_task_storage_busy);
this_cpu_inc(bpf_task_storage_busy);
}
static void bpf_task_storage_unlock(void)
{
__this_cpu_dec(bpf_task_storage_busy);
this_cpu_dec(bpf_task_storage_busy);
migrate_enable();
}
static bool bpf_task_storage_trylock(void)
{
migrate_disable();
if (unlikely(__this_cpu_inc_return(bpf_task_storage_busy) != 1)) {
__this_cpu_dec(bpf_task_storage_busy);
if (unlikely(this_cpu_inc_return(bpf_task_storage_busy) != 1)) {
this_cpu_dec(bpf_task_storage_busy);
migrate_enable();
return false;
}