>Subject: [PATCH 2/3] srcu: protect against concurrent srcu_gp_end()
>
>At present, the code chunk "Transition to big if needed" is out of the
>lock srcu_cb_mutex, which allows the following scene:
>
> srcu_gp_end() on cpu1 srcu_gp_end() on cpu2
>
> init_srcu_struct_nodes()
> ^^ scheduled out in the middle
> init_srcu_struct_nodes()
> ^^ overwrite the context set up by cpu1
Hi Pingfan
This scenario shouldn't happen.
The srcu_gp_end() is invoked only in process_srcu() workfn.
for the same ssp->work, workqueue can guaranteed that the
process_srcu() workfn is executed serially. (view __queue_work () details)
Thanks
Zqiang
>
>Squashing out the race window by putting the code chunk under the
>protection of srcu_cb_mutex.
>
>Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
>Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
>Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
>Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
>Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>Cc: "Zhang, Qiang1" <qiang1.zhang@xxxxxxxxx>
>To: rcu@xxxxxxxxxxxxxxx
>---
> kernel/rcu/srcutree.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
>diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
>index fe0759d89c2d..281cd69fe804 100644
>--- a/kernel/rcu/srcutree.c
>+++ b/kernel/rcu/srcutree.c
>@@ -811,6 +811,13 @@ static void srcu_gp_end(struct srcu_struct *ssp)
> spin_unlock_irqrestore_rcu_node(sdp, flags);
> }
>
>+ /* Transition to big if needed. */
>+ if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
>+ if (ss_state == SRCU_SIZE_ALLOC)
>+ init_srcu_struct_nodes(ssp, GFP_KERNEL);
>+ else
>+ smp_store_release(&ssp->srcu_size_state, ss_state + 1);
>+ }
> /* Callback initiation done, allow grace periods after next. */
> mutex_unlock(&ssp->srcu_cb_mutex);
>
>@@ -826,13 +833,6 @@ static void srcu_gp_end(struct srcu_struct *ssp)
> spin_unlock_irq_rcu_node(ssp);
> }
>
>- /* Transition to big if needed. */
>- if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) {
>- if (ss_state == SRCU_SIZE_ALLOC)
>- init_srcu_struct_nodes(ssp, GFP_KERNEL);
>- else
>- smp_store_release(&ssp->srcu_size_state, ss_state + 1);
>- }
> }
>
> /*
>--
>2.31.1
>
