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bpf: replace bpf_timer_cancel_and_free with a generic helper

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Same reason than most bpf_timer* functions, we need almost the same for
workqueues.
So extract the generic part out of it so bpf_wq_cancel_and_free can reuse
it.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Link: https://lore.kernel.org/r/20240420-bpf_wq-v2-4-6c986a5a741f@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Benjamin Tissoires 2024-04-20 11:09:04 +02:00 committed by Alexei Starovoitov
parent 073f11b026
commit fc22d9495f
1 changed files with 26 additions and 18 deletions
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44
kernel/bpf/helpers.c
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@ -1413,36 +1413,44 @@ static const struct bpf_func_proto bpf_timer_cancel_proto = {
.arg1_type = ARG_PTR_TO_TIMER,
};
static struct bpf_async_cb *__bpf_async_cancel_and_free(struct bpf_async_kern *async)
{
struct bpf_async_cb *cb;
/* Performance optimization: read async->cb without lock first. */
if (!READ_ONCE(async->cb))
return NULL;
__bpf_spin_lock_irqsave(&async->lock);
/* re-read it under lock */
cb = async->cb;
if (!cb)
goto out;
drop_prog_refcnt(cb);
/* The subsequent bpf_timer_start/cancel() helpers won't be able to use
* this timer, since it won't be initialized.
*/
WRITE_ONCE(async->cb, NULL);
out:
__bpf_spin_unlock_irqrestore(&async->lock);
return cb;
}
/* This function is called by map_delete/update_elem for individual element and
* by ops->map_release_uref when the user space reference to a map reaches zero.
*/
void bpf_timer_cancel_and_free(void *val)
{
struct bpf_async_kern *timer = val;
struct bpf_hrtimer *t;
/* Performance optimization: read timer->timer without lock first. */
if (!READ_ONCE(timer->timer))
return;
t = (struct bpf_hrtimer *)__bpf_async_cancel_and_free(val);
__bpf_spin_lock_irqsave(&timer->lock);
/* re-read it under lock */
t = timer->timer;
if (!t)
goto out;
drop_prog_refcnt(&t->cb);
/* The subsequent bpf_timer_start/cancel() helpers won't be able to use
* this timer, since it won't be initialized.
*/
WRITE_ONCE(timer->timer, NULL);
out:
__bpf_spin_unlock_irqrestore(&timer->lock);
if (!t)
return;
/* Cancel the timer and wait for callback to complete if it was running.
* If hrtimer_cancel() can be safely called it's safe to call kfree(t)
* right after for both preallocated and non-preallocated maps.
* The timer->timer = NULL was already done and no code path can
* The async->cb = NULL was already done and no code path can
* see address 't' anymore.
*
* Check that bpf_map_delete/update_elem() wasn't called from timer
@ -1451,7 +1459,7 @@ out:
* return -1). Though callback_fn is still running on this cpu it's
* safe to do kfree(t) because bpf_timer_cb() read everything it needed
* from 't'. The bpf subprog callback_fn won't be able to access 't',
* since timer->timer = NULL was already done. The timer will be
* since async->cb = NULL was already done. The timer will be
* effectively cancelled because bpf_timer_cb() will return
* HRTIMER_NORESTART.
*/