On Mon, Aug 10, 2026 at 06:55:22PM +0800, Zqiang wrote:
> The WARN_ON() for timer_delete_sync() means that the caller forgot to
> call srcu_barrier() before cleanup. however, it still can trigger even
> when srcu_barrier() was properly called.
>
> When a SRCU grace period ends and ss_state < SRCU_SIZE_BIG, the mask=~0
> causes delay_work timer be queued on every online CPU regardless of
> whether it's sdp->srcu_cblist has callbacks. srcu_barrier() only wait
> srcu_barrier_head's callbacks to complete, however, the srcu_barrier_head
> will not be inserted into an empty sdp->srcu_cblist. after that, when
> cleanup_srcu_struct() finds a pending delay_work timer on a CPU with no
> callbacks, triggering a false positive.
>
> This commit therefore add rcu_segcblist_n_cbs() to WARN_ON(), make the
> warning triggers only when the timer is still pending and there are actual
> outstanding callbacks.
>
> Fixes: 05c3e88488ed ("srcu: Queue sdp->work when the delay timer is
> successfully deleted")
> Reported-by: Breno Leitao <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> Closes: https://lore.kernel.org/oe-lkp/[email protected]/
> Tested-by: kernel test robot <[email protected]>
> Signed-off-by: Zqiang <[email protected]>
> ---
> kernel/rcu/srcutree.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 35fface51d50..090dddfc7463 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -753,8 +753,9 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
>
> // Call srcu_barrier() before this cleanup_srcu_struct()
> // to avoid triggering this WARN_ON().
> - if (WARN_ON(timer_delete_sync(&sdp->delay_work)) &&
> - rcu_cpu_beenfullyonline(sdp->cpu))
> + if (WARN_ON(timer_delete_sync(&sdp->delay_work) &&
> + rcu_segcblist_n_cbs(&sdp->srcu_cblist)) &&
> + rcu_cpu_beenfullyonline(sdp->cpu))
This is quite hard to read, mainly with this indentation.
You probably want to rewrite the checks , otherwise the indentation
should be something like, which is horrible (although correct?):
if (WARN_ON(timer_delete_sync(&sdp->delay_work) &&
rcu_segcblist_n_cbs(&sdp->srcu_cblist)) &&
rcu_cpu_beenfullyonline(sdp->cpu))
Would something like this work?
if (rcu_cpu_beenfullyonline(sdp->cpu) &&
WARN_ON(timer_delete_sync(&sdp->delay_work) &&
rcu_segcblist_n_cbs(&sdp->srcu_cblist)))
