New helper legitimize_mntget for getting a mnt without setting
MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED, otherwise return NULL.
v9, Update using read_seqbegin_or_lock instead read_seqlock_excl
v10, fix bad logical of using seqlock
Signed-off-by: Kinglong Mee <kinglongmee@xxxxxxxxx>
---
fs/namespace.c | 38 ++++++++++++++++++++++++++++++++++++++
include/linux/mount.h | 1 +
2 files changed, 39 insertions(+)
diff --git a/fs/namespace.c b/fs/namespace.c
index 0570729..6377672 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1153,6 +1153,44 @@ struct vfsmount *mntget(struct vfsmount *mnt)
}
EXPORT_SYMBOL(mntget);
+struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt)
+{
+ struct mount *mnt;
+ unsigned seq = 0;
+
+ if (vfsmnt == NULL)
+ return NULL;
+
+ rcu_read_lock();
+retry:
+ read_seqbegin_or_lock(&mount_lock, &seq);
+
+ if (vfsmnt->mnt_flags & (MNT_SYNC_UMOUNT | MNT_UMOUNT | MNT_DOOMED))
+ vfsmnt = NULL;
+ else {
+ mnt = real_mount(vfsmnt);
+ mnt_add_count(mnt, 1);
+ if (need_seqretry(&mount_lock, seq)) {
+ /* lost the race, need to try again */
+ if (vfsmnt->mnt_flags & MNT_SYNC_UMOUNT) {
+ /* no point trying... */
+ mnt_add_count(mnt, -1);
+ vfsmnt = NULL;
+ } else {
+ mntput(vfsmnt);
+ seq = 1;
+ goto retry;
+ }
+ }
+ }
+
+ done_seqretry(&mount_lock, seq);
+ rcu_read_unlock();
+
+ return vfsmnt;
+}
+EXPORT_SYMBOL(legitimize_mntget);
+
struct vfsmount *mnt_clone_internal(struct path *path)
{
struct mount *p;
diff --git a/include/linux/mount.h b/include/linux/mount.h
index f822c3c..8ae9dc0 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -79,6 +79,7 @@ extern void mnt_drop_write(struct vfsmount *mnt);
extern void mnt_drop_write_file(struct file *file);
extern void mntput(struct vfsmount *mnt);
extern struct vfsmount *mntget(struct vfsmount *mnt);
+extern struct vfsmount *legitimize_mntget(struct vfsmount *vfsmnt);
extern struct vfsmount *mnt_clone_internal(struct path *path);
extern int __mnt_is_readonly(struct vfsmount *mnt);
--
2.4.3
--
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