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authorAl Viro <viro@zeniv.linux.org.uk>2011-01-15 06:30:21 +0300
committerAl Viro <viro@zeniv.linux.org.uk>2011-01-16 21:47:07 +0300
commitf03c65993b98eeb909a4012ce7833c5857d74755 (patch)
treea6dd5e353889b7fe4ab87c54170d09443d788fec /include/linux/mount.h
parent7b8a53fd815deb39542085897743fa0063f9fe06 (diff)
downloadlinux-f03c65993b98eeb909a4012ce7833c5857d74755.tar.xz
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 'include/linux/mount.h')
-rw-r--r--include/linux/mount.h4
1 files changed, 1 insertions, 3 deletions
diff --git a/include/linux/mount.h b/include/linux/mount.h
index af4765ea8fde..604f122a2326 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -60,7 +60,7 @@ struct vfsmount {
struct super_block *mnt_sb; /* pointer to superblock */
#ifdef CONFIG_SMP
struct mnt_pcp __percpu *mnt_pcp;
- atomic_t mnt_longrefs;
+ atomic_t mnt_longterm; /* how many of the refs are longterm */
#else
int mnt_count;
int mnt_writers;
@@ -96,8 +96,6 @@ extern int mnt_clone_write(struct vfsmount *mnt);
extern void mnt_drop_write(struct vfsmount *mnt);
extern void mntput(struct vfsmount *mnt);
extern struct vfsmount *mntget(struct vfsmount *mnt);
-extern void mntput_long(struct vfsmount *mnt);
-extern struct vfsmount *mntget_long(struct vfsmount *mnt);
extern void mnt_pin(struct vfsmount *mnt);
extern void mnt_unpin(struct vfsmount *mnt);
extern int __mnt_is_readonly(struct vfsmount *mnt);