summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorMiklos Szeredi <mszeredi@redhat.com>2020-06-04 11:48:19 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2020-06-04 11:48:19 +0300
commitdf820f8de4e481222b17f9bcee7b909ae8167529 (patch)
tree8410725a7cd85f540f59120710b8617c18348670
parentb8e42a651bdee06202ebdd96cff64fdeabd5b1d6 (diff)
downloadlinux-df820f8de4e481222b17f9bcee7b909ae8167529.tar.xz
ovl: make private mounts longterm
Overlayfs is using clone_private_mount() to create internal mounts for underlying layers. These are used for operations requiring a path, such as dentry_open(). Since these private mounts are not in any namespace they are treated as short term, "detached" mounts and mntput() involves taking the global mount_lock, which can result in serious cacheline pingpong. Make these private mounts longterm instead, which trade the penalty on mntput() for a slightly longer shutdown time due to an added RCU grace period when putting these mounts. Introduce a new helper kern_unmount_many() that can take care of multiple longterm mounts with a single RCU grace period. Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
-rw-r--r--Documentation/filesystems/porting.rst7
-rw-r--r--fs/namespace.c16
-rw-r--r--fs/overlayfs/super.c7
-rw-r--r--include/linux/mount.h2
4 files changed, 31 insertions, 1 deletions
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 26c093969573..867036aa90b8 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -858,3 +858,10 @@ be misspelled d_alloc_anon().
[should've been added in 2016] stale comment in finish_open() nonwithstanding,
failure exits in ->atomic_open() instances should *NOT* fput() the file,
no matter what. Everything is handled by the caller.
+
+---
+
+**mandatory**
+
+clone_private_mount() returns a longterm mount now, so the proper destructor of
+its result is kern_unmount() or kern_unmount_array().
diff --git a/fs/namespace.c b/fs/namespace.c
index a28e4db075ed..d53517f1d741 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1879,6 +1879,9 @@ struct vfsmount *clone_private_mount(const struct path *path)
if (IS_ERR(new_mnt))
return ERR_CAST(new_mnt);
+ /* Longterm mount to be removed by kern_unmount*() */
+ new_mnt->mnt_ns = MNT_NS_INTERNAL;
+
return &new_mnt->mnt;
}
EXPORT_SYMBOL_GPL(clone_private_mount);
@@ -3804,6 +3807,19 @@ void kern_unmount(struct vfsmount *mnt)
}
EXPORT_SYMBOL(kern_unmount);
+void kern_unmount_array(struct vfsmount *mnt[], unsigned int num)
+{
+ unsigned int i;
+
+ for (i = 0; i < num; i++)
+ if (mnt[i])
+ real_mount(mnt[i])->mnt_ns = NULL;
+ synchronize_rcu_expedited();
+ for (i = 0; i < num; i++)
+ mntput(mnt[i]);
+}
+EXPORT_SYMBOL(kern_unmount_array);
+
bool our_mnt(struct vfsmount *mnt)
{
return check_mnt(real_mount(mnt));
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index eb81d8760a6a..8d8cd46e1482 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -211,6 +211,7 @@ static void ovl_destroy_inode(struct inode *inode)
static void ovl_free_fs(struct ovl_fs *ofs)
{
+ struct vfsmount **mounts;
unsigned i;
iput(ofs->workbasedir_trap);
@@ -224,10 +225,14 @@ static void ovl_free_fs(struct ovl_fs *ofs)
dput(ofs->workbasedir);
if (ofs->upperdir_locked)
ovl_inuse_unlock(ovl_upper_mnt(ofs)->mnt_root);
+
+ /* Hack! Reuse ofs->layers as a vfsmount array before freeing it */
+ mounts = (struct vfsmount **) ofs->layers;
for (i = 0; i < ofs->numlayer; i++) {
iput(ofs->layers[i].trap);
- mntput(ofs->layers[i].mnt);
+ mounts[i] = ofs->layers[i].mnt;
}
+ kern_unmount_array(mounts, ofs->numlayer);
kfree(ofs->layers);
for (i = 0; i < ofs->numfs; i++)
free_anon_bdev(ofs->fs[i].pseudo_dev);
diff --git a/include/linux/mount.h b/include/linux/mount.h
index bf8cc4108b8f..8de95a0bec8d 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -109,4 +109,6 @@ extern unsigned int sysctl_mount_max;
extern bool path_is_mountpoint(const struct path *path);
+extern void kern_unmount_array(struct vfsmount *mnt[], unsigned int num);
+
#endif /* _LINUX_MOUNT_H */