srcu: Prevent cleanup_srcu_struct() from freeing non-dynamic ->sda

When an srcu_struct structure is created (but not in a kernel module)
by DEFINE_SRCU() and friends, the per-CPU srcu_data structure is
statically allocated.  In all other cases, that structure is obtained
from alloc_percpu(), in which case cleanup_srcu_struct() must invoke
free_percpu() on the resulting ->sda pointer in the srcu_struct pointer.

Which it does.

Except that it also invokes free_percpu() on the ->sda pointer
referencing the statically allocated per-CPU srcu_data structures.
Which free_percpu() is surprisingly OK with.

This commit nevertheless stops cleanup_srcu_struct() from freeing
statically allocated per-CPU srcu_data structures.

Co-developed-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 44e9986..44bd204 100644 (file)
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -73,6 +73,7 @@ struct srcu_struct {
        unsigned long srcu_gp_seq_needed_exp;   /* Furthest future exp GP. */
        unsigned long srcu_last_gp_end;         /* Last GP end timestamp (ns) */
        struct srcu_data __percpu *sda;         /* Per-CPU srcu_data array. */
+       bool sda_is_static;                     /* May ->sda be passed to free_percpu()? */
        unsigned long srcu_barrier_seq;         /* srcu_barrier seq #. */
        struct mutex srcu_barrier_mutex;        /* Serialize barrier ops. */
        struct completion srcu_barrier_completion;

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index b7138db..7209fd9 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -217,6 +217,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
        mutex_init(&ssp->srcu_barrier_mutex);
        atomic_set(&ssp->srcu_barrier_cpu_cnt, 0);
        INIT_DELAYED_WORK(&ssp->work, process_srcu);
+       ssp->sda_is_static = is_static;
        if (!is_static)
                ssp->sda = alloc_percpu(struct srcu_data);
        if (!ssp->sda)
@@ -226,7 +227,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
        ssp->srcu_last_gp_end = ktime_get_mono_fast_ns();
        if (READ_ONCE(ssp->srcu_size_state) == SRCU_SIZE_SMALL && convert_to_big == 1) {
                if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) {
-                       if (!is_static) {
+                       if (!ssp->sda_is_static) {
                                free_percpu(ssp->sda);
                                ssp->sda = NULL;
                                return -ENOMEM;
@@ -446,8 +447,10 @@ void cleanup_srcu_struct(struct srcu_struct *ssp)
                        rcu_seq_current(&ssp->srcu_gp_seq), ssp->srcu_gp_seq_needed);
                return; /* Caller forgot to stop doing call_srcu()? */
        }
-       free_percpu(ssp->sda);
-       ssp->sda = NULL;
+       if (!ssp->sda_is_static) {
+               free_percpu(ssp->sda);
+               ssp->sda = NULL;
+       }
        kfree(ssp->node);
        ssp->node = NULL;
        ssp->srcu_size_state = SRCU_SIZE_SMALL;