[PATCH 4.14 072/159] locking/barriers: Convert users of lockless_dereference() to READ_ONCE()

Greg Kroah-Hartman
2017-12-22T09:01:56Z

From: Will Deacon <will.deacon@arm.com>

commit 3382290ed2d5e275429cef510ab21889d3ccd164 upstream.

[ Note, this is a Git cherry-pick of the following commit:

506458efaf15 ("locking/barriers: Convert users of lockless_dereference() to READ_ONCE()")

... for easier x86 PTI code testing and back-porting. ]

READ_ONCE() now has an implicit smp_read_barrier_depends() call, so it
can be used instead of lockless_dereference() without any change in
semantics.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1508840570-22169-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/events/core.c | 2 +-
arch/x86/include/asm/mmu_context.h | 4 ++--
arch/x86/kernel/ldt.c | 2 +-
drivers/md/dm-mpath.c | 20 ++++++++++----------
fs/dcache.c | 4 ++--
fs/overlayfs/ovl_entry.h | 2 +-
fs/overlayfs/readdir.c | 2 +-
include/linux/rculist.h | 4 ++--
include/linux/rcupdate.h | 4 ++--
kernel/events/core.c | 4 ++--
kernel/seccomp.c | 2 +-
kernel/task_work.c | 2 +-
mm/slab.h | 2 +-
13 files changed, 27 insertions(+), 27 deletions(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2371,7 +2371,7 @@ static unsigned long get_segment_base(un
struct ldt_struct *ldt;

/* IRQs are off, so this synchronizes with smp_store_release */
- ldt = lockless_dereference(current->active_mm->context.ldt);
+ ldt = READ_ONCE(current->active_mm->context.ldt);
if (!ldt || idx >= ldt->nr_entries)
return 0;

--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -73,8 +73,8 @@ static inline void load_mm_ldt(struct mm
#ifdef CONFIG_MODIFY_LDT_SYSCALL
struct ldt_struct *ldt;

- /* lockless_dereference synchronizes with smp_store_release */
- ldt = lockless_dereference(mm->context.ldt);
+ /* READ_ONCE synchronizes with smp_store_release */
+ ldt = READ_ONCE(mm->context.ldt);

/*
* Any change to mm->context.ldt is followed by an IPI to all
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -103,7 +103,7 @@ static void finalize_ldt_struct(struct l
static void install_ldt(struct mm_struct *current_mm,
struct ldt_struct *ldt)
{
- /* Synchronizes with lockless_dereference in load_mm_ldt. */
+ /* Synchronizes with READ_ONCE in load_mm_ldt. */
smp_store_release(&current_mm->context.ldt, ldt);

/* Activate the LDT for all CPUs using current_mm. */
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -366,7 +366,7 @@ static struct pgpath *choose_path_in_pg(

pgpath = path_to_pgpath(path);

- if (unlikely(lockless_dereference(m->current_pg) != pg)) {
+ if (unlikely(READ_ONCE(m->current_pg) != pg)) {
/* Only update current_pgpath if pg changed */
spin_lock_irqsave(&m->lock, flags);
m->current_pgpath = pgpath;
@@ -390,7 +390,7 @@ static struct pgpath *choose_pgpath(stru
}

/* Were we instructed to switch PG? */
- if (lockless_dereference(m->next_pg)) {
+ if (READ_ONCE(m->next_pg)) {
spin_lock_irqsave(&m->lock, flags);
pg = m->next_pg;
if (!pg) {
@@ -406,7 +406,7 @@ static struct pgpath *choose_pgpath(stru

/* Don't change PG until it has no remaining paths */
check_current_pg:
- pg = lockless_dereference(m->current_pg);
+ pg = READ_ONCE(m->current_pg);
if (pg) {
pgpath = choose_path_in_pg(m, pg, nr_bytes);
if (!IS_ERR_OR_NULL(pgpath))
@@ -473,7 +473,7 @@ static int multipath_clone_and_map(struc
struct request *clone;

/* Do we need to select a new pgpath? */
- pgpath = lockless_dereference(m->current_pgpath);
+ pgpath = READ_ONCE(m->current_pgpath);
if (!pgpath || !test_bit(MPATHF_QUEUE_IO, &m->flags))
pgpath = choose_pgpath(m, nr_bytes);

@@ -533,7 +533,7 @@ static int __multipath_map_bio(struct mu
bool queue_io;

/* Do we need to select a new pgpath? */
- pgpath = lockless_dereference(m->current_pgpath);
+ pgpath = READ_ONCE(m->current_pgpath);
queue_io = test_bit(MPATHF_QUEUE_IO, &m->flags);
if (!pgpath || !queue_io)
pgpath = choose_pgpath(m, nr_bytes);
@@ -1802,7 +1802,7 @@ static int multipath_prepare_ioctl(struc
struct pgpath *current_pgpath;
int r;

- current_pgpath = lockless_dereference(m->current_pgpath);
+ current_pgpath = READ_ONCE(m->current_pgpath);
if (!current_pgpath)
current_pgpath = choose_pgpath(m, 0);

@@ -1824,7 +1824,7 @@ static int multipath_prepare_ioctl(struc
}

if (r == -ENOTCONN) {
- if (!lockless_dereference(m->current_pg)) {
+ if (!READ_ONCE(m->current_pg)) {
/* Path status changed, redo selection */
(void) choose_pgpath(m, 0);
}
@@ -1893,9 +1893,9 @@ static int multipath_busy(struct dm_targ
return (m->queue_mode != DM_TYPE_MQ_REQUEST_BASED);

/* Guess which priority_group will be used at next mapping time */
- pg = lockless_dereference(m->current_pg);
- next_pg = lockless_dereference(m->next_pg);
- if (unlikely(!lockless_dereference(m->current_pgpath) && next_pg))
+ pg = READ_ONCE(m->current_pg);
+ next_pg = READ_ONCE(m->next_pg);
+ if (unlikely(!READ_ONCE(m->current_pgpath) && next_pg))
pg = next_pg;

if (!pg) {
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -231,7 +231,7 @@ static inline int dentry_cmp(const struc
{
/*
* Be careful about RCU walk racing with rename:
- * use 'lockless_dereference' to fetch the name pointer.
+ * use 'READ_ONCE' to fetch the name pointer.
*
* NOTE! Even if a rename will mean that the length
* was not loaded atomically, we don't care. The
@@ -245,7 +245,7 @@ static inline int dentry_cmp(const struc
* early because the data cannot match (there can
* be no NUL in the ct/tcount data)
*/
- const unsigned char *cs = lockless_dereference(dentry->d_name.name);
+ const unsigned char *cs = READ_ONCE(dentry->d_name.name);

return dentry_string_cmp(cs, ct, tcount);
}
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -77,5 +77,5 @@ static inline struct ovl_inode *OVL_I(st

static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
{
- return lockless_dereference(oi->__upperdentry);
+ return READ_ONCE(oi->__upperdentry);
}
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -757,7 +757,7 @@ static int ovl_dir_fsync(struct file *fi
if (!od->is_upper && OVL_TYPE_UPPER(ovl_path_type(dentry))) {
struct inode *inode = file_inode(file);

- realfile = lockless_dereference(od->upperfile);
+ realfile = READ_ONCE(od->upperfile);
if (!realfile) {
struct path upperpath;

--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -275,7 +275,7 @@ static inline void list_splice_tail_init
* primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
*/
#define list_entry_rcu(ptr, type, member) \
- container_of(lockless_dereference(ptr), type, member)
+ container_of(READ_ONCE(ptr), type, member)

/*
* Where are list_empty_rcu() and list_first_entry_rcu()?
@@ -368,7 +368,7 @@ static inline void list_splice_tail_init
* example is when items are added to the list, but never deleted.
*/
#define list_entry_lockless(ptr, type, member) \
- container_of((typeof(ptr))lockless_dereference(ptr), type, member)
+ container_of((typeof(ptr))READ_ONCE(ptr), type, member)

/**
* list_for_each_entry_lockless - iterate over rcu list of given type
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -346,7 +346,7 @@ static inline void rcu_preempt_sleep_che
#define __rcu_dereference_check(p, c, space) \
({ \
/* Dependency order vs. p above. */ \
- typeof(*p) *________p1 = (typeof(*p) *__force)lockless_dereference(p); \
+ typeof(*p) *________p1 = (typeof(*p) *__force)READ_ONCE(p); \
RCU_LOCKDEP_WARN(!(c), "suspicious rcu_dereference_check() usage"); \
rcu_dereference_sparse(p, space); \
((typeof(*p) __force __kernel *)(________p1)); \
@@ -360,7 +360,7 @@ static inline void rcu_preempt_sleep_che
#define rcu_dereference_raw(p) \
({ \
/* Dependency order vs. p above. */ \
- typeof(p) ________p1 = lockless_dereference(p); \
+ typeof(p) ________p1 = READ_ONCE(p); \
((typeof(*p) __force __kernel *)(________p1)); \
})

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4233,7 +4233,7 @@ static void perf_remove_from_owner(struc
* indeed free this event, otherwise we need to serialize on
* owner->perf_event_mutex.
*/
- owner = lockless_dereference(event->owner);
+ owner = READ_ONCE(event->owner);
if (owner) {
/*
* Since delayed_put_task_struct() also drops the last
@@ -4330,7 +4330,7 @@ again:
* Cannot change, child events are not migrated, see the
* comment with perf_event_ctx_lock_nested().
*/
- ctx = lockless_dereference(child->ctx);
+ ctx = READ_ONCE(child->ctx);
/*
* Since child_mutex nests inside ctx::mutex, we must jump
* through hoops. We start by grabbing a reference on the ctx.
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -190,7 +190,7 @@ static u32 seccomp_run_filters(const str
u32 ret = SECCOMP_RET_ALLOW;
/* Make sure cross-thread synced filter points somewhere sane. */
struct seccomp_filter *f =
- lockless_dereference(current->seccomp.filter);
+ READ_ONCE(current->seccomp.filter);

/* Ensure unexpected behavior doesn't result in failing open. */
if (unlikely(WARN_ON(f == NULL)))
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -68,7 +68,7 @@ task_work_cancel(struct task_struct *tas
* we raced with task_work_run(), *pprev == NULL/exited.
*/
raw_spin_lock_irqsave(&task->pi_lock, flags);
- while ((work = lockless_dereference(*pprev))) {
+ while ((work = READ_ONCE(*pprev))) {
if (work->func != func)
pprev = &work->next;
else if (cmpxchg(pprev, work, work->next) == work)
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -259,7 +259,7 @@ cache_from_memcg_idx(struct kmem_cache *
* memcg_caches issues a write barrier to match this (see
* memcg_create_kmem_cache()).
*/
- cachep = lockless_dereference(arr->entries[idx]);
+ cachep = READ_ONCE(arr->entries[idx]);
rcu_read_unlock();

return cachep;