path: root/fs/internal.h
diff options
authorAl Viro <viro@zeniv.linux.org.uk>2011-01-14 22:30:21 -0500
committerAl Viro <viro@zeniv.linux.org.uk>2011-01-16 13:47:07 -0500
commitf03c65993b98eeb909a4012ce7833c5857d74755 (patch)
treea6dd5e353889b7fe4ab87c54170d09443d788fec /fs/internal.h
parent7b8a53fd815deb39542085897743fa0063f9fe06 (diff)
sanitize vfsmount refcounting changes
Instead of splitting refcount between (per-cpu) mnt_count and (SMP-only) mnt_longrefs, make all references contribute to mnt_count again and keep track of how many are longterm ones. Accounting rules for longterm count: * 1 for each fs_struct.root.mnt * 1 for each fs_struct.pwd.mnt * 1 for having non-NULL ->mnt_ns * decrement to 0 happens only under vfsmount lock exclusive That allows nice common case for mntput() - since we can't drop the final reference until after mnt_longterm has reached 0 due to the rules above, mntput() can grab vfsmount lock shared and check mnt_longterm. If it turns out to be non-zero (which is the common case), we know that this is not the final mntput() and can just blindly decrement percpu mnt_count. Otherwise we grab vfsmount lock exclusive and do usual decrement-and-check of percpu mnt_count. For fs_struct.c we have mnt_make_longterm() and mnt_make_shortterm(); namespace.c uses the latter in places where we don't already hold vfsmount lock exclusive and opencodes a few remaining spots where we need to manipulate mnt_longterm. Note that we mostly revert the code outside of fs/namespace.c back to what we used to have; in particular, normal code doesn't need to care about two kinds of references, etc. And we get to keep the optimization Nick's variant had bought us... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/internal.h')
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/internal.h b/fs/internal.h
index 4931060fd08..12ccb86edef 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -73,6 +73,9 @@ extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
extern int do_add_mount(struct vfsmount *, struct path *, int);
extern void mnt_clear_expiry(struct vfsmount *);
+extern void mnt_make_longterm(struct vfsmount *);
+extern void mnt_make_shortterm(struct vfsmount *);
extern void __init mnt_init(void);