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author | Al Viro <viro@zeniv.linux.org.uk> | 2011-01-15 04:30:21 +0100 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2011-01-16 19:47:07 +0100 |
commit | f03c65993b98eeb909a4012ce7833c5857d74755 (patch) | |
tree | a6dd5e353889b7fe4ab87c54170d09443d788fec /fs/fs_struct.c | |
parent | fix old umount_tree() breakage (diff) | |
download | linux-f03c65993b98eeb909a4012ce7833c5857d74755.tar.xz linux-f03c65993b98eeb909a4012ce7833c5857d74755.zip |
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/fs_struct.c')
-rw-r--r-- | fs/fs_struct.c | 35 |
1 files changed, 24 insertions, 11 deletions
diff --git a/fs/fs_struct.c b/fs/fs_struct.c index 68ca487bedb1..78b519c13536 100644 --- a/fs/fs_struct.c +++ b/fs/fs_struct.c @@ -4,6 +4,19 @@ #include <linux/path.h> #include <linux/slab.h> #include <linux/fs_struct.h> +#include "internal.h" + +static inline void path_get_longterm(struct path *path) +{ + path_get(path); + mnt_make_longterm(path->mnt); +} + +static inline void path_put_longterm(struct path *path) +{ + mnt_make_shortterm(path->mnt); + path_put(path); +} /* * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values. @@ -17,11 +30,11 @@ void set_fs_root(struct fs_struct *fs, struct path *path) write_seqcount_begin(&fs->seq); old_root = fs->root; fs->root = *path; - path_get_long(path); + path_get_longterm(path); write_seqcount_end(&fs->seq); spin_unlock(&fs->lock); if (old_root.dentry) - path_put_long(&old_root); + path_put_longterm(&old_root); } /* @@ -36,12 +49,12 @@ void set_fs_pwd(struct fs_struct *fs, struct path *path) write_seqcount_begin(&fs->seq); old_pwd = fs->pwd; fs->pwd = *path; - path_get_long(path); + path_get_longterm(path); write_seqcount_end(&fs->seq); spin_unlock(&fs->lock); if (old_pwd.dentry) - path_put_long(&old_pwd); + path_put_longterm(&old_pwd); } void chroot_fs_refs(struct path *old_root, struct path *new_root) @@ -59,13 +72,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root) write_seqcount_begin(&fs->seq); if (fs->root.dentry == old_root->dentry && fs->root.mnt == old_root->mnt) { - path_get_long(new_root); + path_get_longterm(new_root); fs->root = *new_root; count++; } if (fs->pwd.dentry == old_root->dentry && fs->pwd.mnt == old_root->mnt) { - path_get_long(new_root); + path_get_longterm(new_root); fs->pwd = *new_root; count++; } @@ -76,13 +89,13 @@ void chroot_fs_refs(struct path *old_root, struct path *new_root) } while_each_thread(g, p); read_unlock(&tasklist_lock); while (count--) - path_put_long(old_root); + path_put_longterm(old_root); } void free_fs_struct(struct fs_struct *fs) { - path_put_long(&fs->root); - path_put_long(&fs->pwd); + path_put_longterm(&fs->root); + path_put_longterm(&fs->pwd); kmem_cache_free(fs_cachep, fs); } @@ -118,9 +131,9 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old) spin_lock(&old->lock); fs->root = old->root; - path_get_long(&fs->root); + path_get_longterm(&fs->root); fs->pwd = old->pwd; - path_get_long(&fs->pwd); + path_get_longterm(&fs->pwd); spin_unlock(&old->lock); } return fs; |