Re: [PATCH v2] srcu: Fix WARN_ON() for timer_delete_sync() in cleanup_srcu_struct()

[Paul E. McKenney]

On Wed, Aug 12, 2026 at 02:07:13AM -0700, Breno Leitao wrote:
> On Tue, Aug 11, 2026 at 08:29:51AM +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 find that the allocation of srcu_node
> > tree has been completed, but the ss_state is still less than SRCU_SIZE_BIG,
> > the mask=~0 causes delay_work timer be queued on every CPU which has
> > been online regardless of whether it's sdp->srcu_cblist has callbacks.
> > the 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 <leitao@xxxxxxxxxx>
> > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-lkp/202608060833.bce92909-lkp@xxxxxxxxx/
> > Tested-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxx>
> 
> Tested-by: Breno Leitao <leitao@xxxxxxxxxx>

Thank you, Breno!  I will add this to the original, which I merged this
fix into.

							Thanx, Paul