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author | Miklos Szeredi <mszeredi@suse.cz> | 2013-09-05 13:44:36 +0400 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2013-09-06 00:23:41 +0400 |
commit | 848ac114e847af3f1f9141c90a39ebe79bdb13b3 (patch) | |
tree | 3673b97171b0e0bc5b179908b4ad15ede9a91b35 /fs/dcache.c | |
parent | db14fc3abcd5dcc9b32ad5b9dd5b8f9e16295a39 (diff) | |
download | linux-848ac114e847af3f1f9141c90a39ebe79bdb13b3.tar.xz |
vfs: check submounts and drop atomically
We check submounts before doing d_drop() on a non-empty directory dentry in
NFS (have_submounts()), but we do not exclude a racing mount.
Process A: have_submounts() -> returns false
Process B: mount() -> success
Process A: d_drop()
This patch prepares the ground for the fix by doing the following
operations all under the same rename lock:
have_submounts()
shrink_dcache_parent()
d_drop()
This is actually an optimization since have_submounts() and
shrink_dcache_parent() both traverse the same dentry tree separately.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
CC: David Howells <dhowells@redhat.com>
CC: Steven Whitehouse <swhiteho@redhat.com>
CC: Trond Myklebust <Trond.Myklebust@netapp.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/dcache.c')
-rw-r--r-- | fs/dcache.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/fs/dcache.c b/fs/dcache.c index 043c5b478a77..ce5a7e6d84cd 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1264,6 +1264,71 @@ void shrink_dcache_parent(struct dentry *parent) } EXPORT_SYMBOL(shrink_dcache_parent); +static enum d_walk_ret check_and_collect(void *_data, struct dentry *dentry) +{ + struct select_data *data = _data; + + if (d_mountpoint(dentry)) { + data->found = -EBUSY; + return D_WALK_QUIT; + } + + return select_collect(_data, dentry); +} + +static void check_and_drop(void *_data) +{ + struct select_data *data = _data; + + if (d_mountpoint(data->start)) + data->found = -EBUSY; + if (!data->found) + __d_drop(data->start); +} + +/** + * check_submounts_and_drop - prune dcache, check for submounts and drop + * + * All done as a single atomic operation relative to has_unlinked_ancestor(). + * Returns 0 if successfully unhashed @parent. If there were submounts then + * return -EBUSY. + * + * @dentry: dentry to prune and drop + */ +int check_submounts_and_drop(struct dentry *dentry) +{ + int ret = 0; + + /* Negative dentries can be dropped without further checks */ + if (!dentry->d_inode) { + d_drop(dentry); + goto out; + } + + for (;;) { + struct select_data data; + + INIT_LIST_HEAD(&data.dispose); + data.start = dentry; + data.found = 0; + + d_walk(dentry, &data, check_and_collect, check_and_drop); + ret = data.found; + + if (!list_empty(&data.dispose)) + shrink_dentry_list(&data.dispose); + + if (ret <= 0) + break; + + cond_resched(); + } + +out: + return ret; +} +EXPORT_SYMBOL(check_submounts_and_drop); + /** * __d_alloc - allocate a dcache entry * @sb: filesystem it will belong to |