Commit 46470cf8 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 4a230f80

include/linux/srcutree.h

+1 −0
Original line number Diff line number Diff line
@@ -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;

kernel/rcu/srcutree.c

+6 −3
Original line number Diff line number Diff line
@@ -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()? */

	}

	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;