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author | Al Viro <viro@zeniv.linux.org.uk> | 2011-01-14 22:30:21 -0500 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2011-01-16 13:47:07 -0500 |
commit | f03c65993b98eeb909a4012ce7833c5857d74755 (patch) | |
tree | a6dd5e353889b7fe4ab87c54170d09443d788fec /fs/internal.h | |
parent | 7b8a53fd815deb39542085897743fa0063f9fe06 (diff) | |
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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')
-rw-r--r-- | fs/internal.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/internal.h b/fs/internal.h index 4931060..12ccb86 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); DECLARE_BRLOCK(vfsmount_lock); |