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btrfs: use READ/WRITE_ONCE for fs_devices->read_policy

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Since we can read/modify the value from the sysfs interface concurrently,
it would be better to protect it from compiler optimizations.

Currently, there is only one read policy BTRFS_READ_POLICY_PID available,
so no actual problem can happen now. This is a preparation for the future
expansion.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Naohiro Aota 2024-02-02 13:23:28 +09:00 committed by David Sterba
parent e383e158ed
commit 4dc4a3be6c
2 changed files with 9 additions and 8 deletions
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7
fs/btrfs/sysfs.c
View File

@ -1228,11 +1228,12 @@ static ssize_t btrfs_read_policy_show(struct kobject *kobj,
struct kobj_attribute *a, char *buf)
{
struct btrfs_fs_devices *fs_devices = to_fs_devs(kobj);
const enum btrfs_read_policy policy = READ_ONCE(fs_devices->read_policy);
ssize_t ret = 0;
int i;
for (i = 0; i < BTRFS_NR_READ_POLICY; i++) {
if (fs_devices->read_policy == i)
if (policy == i)
ret += sysfs_emit_at(buf, ret, "%s[%s]",
(ret == 0 ? "" : " "),
btrfs_read_policy_name[i]);
@ -1256,8 +1257,8 @@ static ssize_t btrfs_read_policy_store(struct kobject *kobj,
for (i = 0; i < BTRFS_NR_READ_POLICY; i++) {
if (sysfs_streq(buf, btrfs_read_policy_name[i])) {
if (i != fs_devices->read_policy) {
fs_devices->read_policy = i;
if (i != READ_ONCE(fs_devices->read_policy)) {
WRITE_ONCE(fs_devices->read_policy, i);
btrfs_info(fs_devices->fs_info,
"read policy set to '%s'",
btrfs_read_policy_name[i]);

10
fs/btrfs/volumes.c
View File

@ -5942,6 +5942,7 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
struct btrfs_chunk_map *map, int first,
int dev_replace_is_ongoing)
{
const enum btrfs_read_policy policy = READ_ONCE(fs_info->fs_devices->read_policy);
int i;
int num_stripes;
int preferred_mirror;
@ -5956,13 +5957,12 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
else
num_stripes = map->num_stripes;
switch (fs_info->fs_devices->read_policy) {
switch (policy) {
default:
/* Shouldn't happen, just warn and use pid instead of failing */
btrfs_warn_rl(fs_info,
"unknown read_policy type %u, reset to pid",
fs_info->fs_devices->read_policy);
fs_info->fs_devices->read_policy = BTRFS_READ_POLICY_PID;
btrfs_warn_rl(fs_info, "unknown read_policy type %u, reset to pid",
policy);
WRITE_ONCE(fs_info->fs_devices->read_policy, BTRFS_READ_POLICY_PID);
fallthrough;
case BTRFS_READ_POLICY_PID:
preferred_mirror = first + (current->pid % num_stripes);