Commit 3382290e authored by Will Deacon's avatar Will Deacon Committed by Ingo Molnar
Browse files

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



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

    506458ef ("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: default avatarWill 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: default avatarIngo Molnar <mingo@kernel.org>
parent c2bc6608

arch/x86/events/core.c

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

arch/x86/include/asm/mmu_context.h

+2 −2
Original line number Diff line number Diff line
@@ -73,8 +73,8 @@ 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

arch/x86/kernel/ldt.c

+1 −1
Original line number Diff line number Diff line
@@ -103,7 +103,7 @@ 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(&current_mm->context.ldt, ldt);



	/* Activate the LDT for all CPUs using current_mm. */

drivers/md/dm-mpath.c

+10 −10
Original line number Diff line number Diff line
@@ -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) {

fs/dcache.c

+2 −2
Original line number Diff line number Diff line
@@ -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);

}

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