From 46470cf85d2b61abd37c6f66c4dacc1bc510d10f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 27 Jan 2022 13:20:49 -0800 Subject: 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 Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'kernel/rcu/srcutree.c') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index b7138dbe1a2d..7209fd95dde9 100644 --- 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; -- cgit v1.2.3