srcu: Make early-boot call_srcu() reuse workqueue lists

Allocating a list_head structure that is almost never used, and, when
used, is used only during early boot (rcu_init() and earlier), is a bit
wasteful.  This commit therefore eliminates that list_head in favor of
the one in the work_struct structure.  This is safe because the work_struct
structure cannot be used until after rcu_init() returns.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

2 files changed, 1 insertions, 4 deletions

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 2b5c0822e683..f41d2fb09f87 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -36,7 +36,6 @@ struct srcu_struct {
         struct rcu_head *srcu_cb_head;  /* Pending callbacks: Head. */
         struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
         struct work_struct srcu_work;   /* For driving grace periods. */
-        struct list_head srcu_boot_entry; /* Early-boot callbacks. */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         struct lockdep_map dep_map;
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -49,7 +48,6 @@ void srcu_drive_gp(struct work_struct *wp);
         .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq),        \
         .srcu_cb_tail = &name.srcu_cb_head,                             \
         .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
-        .srcu_boot_entry = LIST_HEAD_INIT(name.srcu_boot_entry),        \
         __SRCU_DEP_MAP_INIT(name)                                       \
 }
 
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 9cfa4610113a..0ae91b3a7406 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -94,7 +94,6 @@ struct srcu_struct {
                                                 /*  callback for the barrier */
                                                 /*  operation. */
         struct delayed_work work;
-        struct list_head srcu_boot_entry;       /* Early-boot callbacks. */
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
         struct lockdep_map dep_map;
 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
@@ -110,7 +109,7 @@ struct srcu_struct {
         .sda = &pcpu_name,                                              \
         .lock = __SPIN_LOCK_UNLOCKED(name.lock),                        \
         .srcu_gp_seq_needed = -1UL,                                     \
-        .srcu_boot_entry = LIST_HEAD_INIT(name.srcu_boot_entry),        \
+        .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0),         \
         __SRCU_DEP_MAP_INIT(name)                                       \
 }