... from ->mnt_flags to LSB of ->mnt_pprev_for_sb.
This is safe - we always set and clear it within the same mount_lock
scope, so we won't interfere with list operations - traversals are
always forward, so they don't even look at ->mnt_prev_for_sb and
both insertions and removals are in mount_lock scopes of their own,
so that bit will be clear in *all* mount instances during those.
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/mount.h | 3 ++-
fs/namespace.c | 50 +++++++++++++++++++++----------------------
include/linux/fs.h | 4 +---
include/linux/mount.h | 3 +--
4 files changed, 29 insertions(+), 31 deletions(-)
diff --git a/fs/mount.h b/fs/mount.h
index 5c2ddcff810c..c13bbd93d837 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -65,7 +65,8 @@ struct mount {
struct list_head mnt_mounts; /* list of children, anchored here */
struct list_head mnt_child; /* and going through their mnt_child */
struct mount *mnt_next_for_sb; /* the next two fields are hlist_node, */
- struct mount **mnt_pprev_for_sb;/* except that LSB of pprev will be stolen */
+ unsigned long mnt_pprev_for_sb; /* except that LSB of pprev is stolen */
+#define WRITE_HOLD 1 /* ... for use by mnt_hold_writers() */
const char *mnt_devname; /* Name of device e.g. /dev/dsk/hda1 */
struct list_head mnt_list;
struct list_head mnt_expire; /* link in fs-specific expiry list */
diff --git a/fs/namespace.c b/fs/namespace.c
index 120854639dd2..f9c9c69a815b 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -509,20 +509,20 @@ int mnt_get_write_access(struct vfsmount *m)
mnt_inc_writers(mnt);
/*
* The store to mnt_inc_writers must be visible before we pass
- * MNT_WRITE_HOLD loop below, so that the slowpath can see our
- * incremented count after it has set MNT_WRITE_HOLD.
+ * WRITE_HOLD loop below, so that the slowpath can see our
+ * incremented count after it has set WRITE_HOLD.
*/
smp_mb();
might_lock(&mount_lock.lock);
- while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
+ while (READ_ONCE(mnt->mnt_pprev_for_sb) & WRITE_HOLD) {
if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
cpu_relax();
} else {
/*
* This prevents priority inversion, if the task
- * setting MNT_WRITE_HOLD got preempted on a remote
+ * setting WRITE_HOLD got preempted on a remote
* CPU, and it prevents life lock if the task setting
- * MNT_WRITE_HOLD has a lower priority and is bound to
+ * WRITE_HOLD has a lower priority and is bound to
* the same CPU as the task that is spinning here.
*/
preempt_enable();
@@ -533,7 +533,7 @@ int mnt_get_write_access(struct vfsmount *m)
}
/*
* The barrier pairs with the barrier sb_start_ro_state_change() making
- * sure that if we see MNT_WRITE_HOLD cleared, we will also see
+ * sure that if we see WRITE_HOLD cleared, we will also see
* s_readonly_remount set (or even SB_RDONLY / MNT_READONLY flags) in
* mnt_is_readonly() and bail in case we are racing with remount
* read-only.
@@ -672,15 +672,15 @@ EXPORT_SYMBOL(mnt_drop_write_file);
* @mnt.
*
* Context: This function expects lock_mount_hash() to be held serializing
- * setting MNT_WRITE_HOLD.
+ * setting WRITE_HOLD.
* Return: On success 0 is returned.
* On error, -EBUSY is returned.
*/
static inline int mnt_hold_writers(struct mount *mnt)
{
- mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
+ mnt->mnt_pprev_for_sb |= WRITE_HOLD;
/*
- * After storing MNT_WRITE_HOLD, we'll read the counters. This store
+ * After storing WRITE_HOLD, we'll read the counters. This store
* should be visible before we do.
*/
smp_mb();
@@ -696,9 +696,9 @@ static inline int mnt_hold_writers(struct mount *mnt)
* sum up each counter, if we read a counter before it is incremented,
* but then read another CPU's count which it has been subsequently
* decremented from -- we would see more decrements than we should.
- * MNT_WRITE_HOLD protects against this scenario, because
+ * WRITE_HOLD protects against this scenario, because
* mnt_want_write first increments count, then smp_mb, then spins on
- * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
+ * WRITE_HOLD, so it can't be decremented by another CPU while
* we're counting up here.
*/
if (mnt_get_writers(mnt) > 0)
@@ -722,20 +722,20 @@ static inline int mnt_hold_writers(struct mount *mnt)
static inline void mnt_unhold_writers(struct mount *mnt)
{
/*
- * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
+ * MNT_READONLY must become visible before ~WRITE_HOLD, so writers
* that become unheld will see MNT_READONLY.
*/
smp_wmb();
- mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+ mnt->mnt_pprev_for_sb &= ~WRITE_HOLD;
}
static inline void mnt_del_instance(struct mount *m)
{
- struct mount **p = m->mnt_pprev_for_sb;
+ struct mount **p = (void *)m->mnt_pprev_for_sb;
struct mount *next = m->mnt_next_for_sb;
if (next)
- next->mnt_pprev_for_sb = p;
+ next->mnt_pprev_for_sb = (unsigned long)p;
*p = next;
}
@@ -744,9 +744,9 @@ static inline void mnt_add_instance(struct mount *m, struct super_block *s)
struct mount *first = s->s_mounts;
if (first)
- first->mnt_pprev_for_sb = &m->mnt_next_for_sb;
+ first->mnt_pprev_for_sb = (unsigned long)&m->mnt_next_for_sb;
m->mnt_next_for_sb = first;
- m->mnt_pprev_for_sb = &s->s_mounts;
+ m->mnt_pprev_for_sb = (unsigned long)&s->s_mounts;
s->s_mounts = m;
}
@@ -765,7 +765,7 @@ int sb_prepare_remount_readonly(struct super_block *sb)
{
int err = 0;
- /* Racy optimization. Recheck the counter under MNT_WRITE_HOLD */
+ /* Racy optimization. Recheck the counter under WRITE_HOLD */
if (atomic_long_read(&sb->s_remove_count))
return -EBUSY;
@@ -783,8 +783,8 @@ int sb_prepare_remount_readonly(struct super_block *sb)
if (!err)
sb_start_ro_state_change(sb);
for (struct mount *m = sb->s_mounts; m; m = m->mnt_next_for_sb) {
- if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
- m->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
+ if (m->mnt_pprev_for_sb & WRITE_HOLD)
+ m->mnt_pprev_for_sb &= ~WRITE_HOLD;
}
unlock_mount_hash();
@@ -4805,18 +4805,18 @@ static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt)
struct mount *p;
/*
- * If we had to call mnt_hold_writers() MNT_WRITE_HOLD will
- * be set in @mnt_flags. The loop unsets MNT_WRITE_HOLD for all
+ * If we had to call mnt_hold_writers() WRITE_HOLD will
+ * be set in @mnt_flags. The loop unsets WRITE_HOLD for all
* mounts and needs to take care to include the first mount.
*/
for (p = mnt; p; p = next_mnt(p, mnt)) {
/* If we had to hold writers unblock them. */
- if (p->mnt.mnt_flags & MNT_WRITE_HOLD)
+ if (p->mnt_pprev_for_sb & WRITE_HOLD)
mnt_unhold_writers(p);
/*
* We're done once the first mount we changed got
- * MNT_WRITE_HOLD unset.
+ * WRITE_HOLD unset.
*/
if (p == m)
break;
@@ -4851,7 +4851,7 @@ static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt)
WRITE_ONCE(m->mnt.mnt_flags, flags);
/* If we had to hold writers unblock them. */
- if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
+ if (mnt->mnt_pprev_for_sb & WRITE_HOLD)
mnt_unhold_writers(m);
if (kattr->propagation)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0e9c7f1460dc..1d583f38fb81 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1324,8 +1324,6 @@ struct sb_writers {
struct percpu_rw_semaphore rw_sem[SB_FREEZE_LEVELS];
};
-struct mount;
-
struct super_block {
struct list_head s_list; /* Keep this first */
dev_t s_dev; /* search index; _not_ kdev_t */
@@ -1360,7 +1358,7 @@ struct super_block {
__u16 s_encoding_flags;
#endif
struct hlist_bl_head s_roots; /* alternate root dentries for NFS */
- struct mount *s_mounts; /* list of mounts; _not_ for fs use */
+ void *s_mounts; /* list of mounts; _not_ for fs use */
struct block_device *s_bdev; /* can go away once we use an accessor for @s_bdev_file */
struct file *s_bdev_file;
struct backing_dev_info *s_bdi;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 18e4b97f8a98..85e97b9340ff 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -33,7 +33,6 @@ enum mount_flags {
MNT_NOSYMFOLLOW = 0x80,
MNT_SHRINKABLE = 0x100,
- MNT_WRITE_HOLD = 0x200,
MNT_INTERNAL = 0x4000,
@@ -52,7 +51,7 @@ enum mount_flags {
| MNT_READONLY | MNT_NOSYMFOLLOW,
MNT_ATIME_MASK = MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME,
- MNT_INTERNAL_FLAGS = MNT_WRITE_HOLD | MNT_INTERNAL | MNT_DOOMED |
+ MNT_INTERNAL_FLAGS = MNT_INTERNAL | MNT_DOOMED |
MNT_SYNC_UMOUNT | MNT_LOCKED
};
--
2.47.2
