Messages in this thread Patch in this message | | | From | Miklos Szeredi <> | Subject | [PATCH 03/11] vfs: check submounts and drop atomically | Date | Thu, 5 Sep 2013 11:44:36 +0200 |
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From: Miklos Szeredi <mszeredi@suse.cz>
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> --- fs/dcache.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++ include/linux/dcache.h | 1 + 2 files changed, 83 insertions(+)
diff --git a/fs/dcache.c b/fs/dcache.c index 3b12076..d05f46c 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1240,6 +1240,88 @@ 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; + } + + spin_lock(&dentry->d_lock); + if (d_unhashed(dentry)) + goto out_unlock; + if (list_empty(&dentry->d_subdirs)) { + if (d_mountpoint(dentry)) { + ret = -EBUSY; + goto out_unlock; + } + __d_drop(dentry); + goto out_unlock; + } + spin_unlock(&dentry->d_lock); + + 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; + +out_unlock: + spin_unlock(&dentry->d_lock); + goto out; +} +EXPORT_SYMBOL(check_submounts_and_drop); + /** * __d_alloc - allocate a dcache entry * @sb: filesystem it will belong to diff --git a/include/linux/dcache.h b/include/linux/dcache.h index efdc944..87bd0d7 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -253,6 +253,7 @@ extern void d_prune_aliases(struct inode *); /* test whether we have any submounts in a subdir tree */ extern int have_submounts(struct dentry *); +extern int check_submounts_and_drop(struct dentry *); /* * This adds the entry to the hash queues. -- 1.8.1.4
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