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Message-Id: <1508840570-22169-4-git-send-email-will.deacon@arm.com>
Date: Tue, 24 Oct 2017 11:22:48 +0100
From: Will Deacon <will.deacon@....com>
To: mingo@...nel.org
Cc: linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH v2 3/5] locking/barriers: Convert users of lockless_dereference() to READ_ONCE()
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.
Cc: Ingo Molnar <mingo@...nel.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Will Deacon <will.deacon@....com>
---
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(-)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 80534d3c2480..589af1eec7c1 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2371,7 +2371,7 @@ static unsigned long get_segment_base(unsigned int segment)
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;
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 3c856a15b98e..efc530642f7d 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -72,8 +72,8 @@ static inline void load_mm_ldt(struct mm_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
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index f0e64db18ac8..0a21390642c4 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -101,7 +101,7 @@ static void finalize_ldt_struct(struct ldt_struct *ldt)
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(¤t_mm->context.ldt, ldt);
/* Activate the LDT for all CPUs using current_mm. */
diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 11f273d2f018..3f88c9d32f7e 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -366,7 +366,7 @@ static struct pgpath *choose_path_in_pg(struct multipath *m,
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(struct multipath *m, size_t nr_bytes)
}
/* 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(struct multipath *m, size_t nr_bytes)
/* 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(struct dm_target *ti, struct request *rq,
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);
@@ -535,7 +535,7 @@ static int __multipath_map_bio(struct multipath *m, struct bio *bio, struct dm_m
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);
@@ -1804,7 +1804,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
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);
@@ -1826,7 +1826,7 @@ static int multipath_prepare_ioctl(struct dm_target *ti,
}
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);
}
@@ -1895,9 +1895,9 @@ static int multipath_busy(struct dm_target *ti)
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) {
diff --git a/fs/dcache.c b/fs/dcache.c
index f90141387f01..34c852af215c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -231,7 +231,7 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
{
/*
* 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 struct dentry *dentry, const unsigned char *c
* 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);
}
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 25d9b5adcd42..36b49bd09264 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -77,5 +77,5 @@ static inline struct ovl_inode *OVL_I(struct inode *inode)
static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
{
- return lockless_dereference(oi->__upperdentry);
+ return READ_ONCE(oi->__upperdentry);
}
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 0f85ee9c3268..c67a7703296b 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -754,7 +754,7 @@ static int ovl_dir_fsync(struct file *file, loff_t start, loff_t end,
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;
diff --git a/include/linux/rculist.h b/include/linux/rculist.h
index 2bea1d5e9930..5ed091c064b2 100644
--- a/include/linux/rculist.h
+++ b/include/linux/rculist.h
@@ -274,7 +274,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
* 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()?
@@ -367,7 +367,7 @@ static inline void list_splice_tail_init_rcu(struct list_head *list,
* 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
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 1a9f70d44af9..a6ddc42f87a5 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -346,7 +346,7 @@ static inline void rcu_preempt_sleep_check(void) { }
#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_check(void) { }
#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)); \
})
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9d93db81fa36..824a583079a1 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4231,7 +4231,7 @@ static void perf_remove_from_owner(struct perf_event *event)
* 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
@@ -4328,7 +4328,7 @@ int perf_event_release_kernel(struct perf_event *event)
* 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.
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 0ae832e13b97..8ac79355915b 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -189,7 +189,7 @@ static u32 seccomp_run_filters(const struct seccomp_data *sd,
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)))
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 836a72a66fba..9a9f262fc53d 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -67,7 +67,7 @@ task_work_cancel(struct task_struct *task, task_work_func_t func)
* 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)
diff --git a/mm/slab.h b/mm/slab.h
index 073362816acc..8894f811a89d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -258,7 +258,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int idx)
* 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;
--
2.1.4
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