>
> 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))
Will update and resend (I still mark v2 because v1 has not been sent before).
Thanks
Zqiang
>
> 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)))
>
