Messages in this thread Patch in this message | | | From | "Hatayama, Daisuke" <> | Subject | [PATCH v2] kernfs: fix dentry unexpected skip | Date | Mon, 21 May 2018 09:11:26 +0000 |
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kernfs_dir_next_pos() overlooks the situation that the dentry corresponding to a given pos object has already been inactive. Hence, when kernfs_dir_pos() returns the dentry with a hash value larger than the original one, kernfs_dir_next_pos() returns the dentry next to the one returned by kernfs_dir_pos(). As a result, the dentry returned by kernfs_dir_pos() is skipped.
To fix this issue, try to find a next node only when the returned object is less than or equal to the original one.
Note that this implementation focuses on getting guarantee that the existing nodes are never skipped, not interested in the other nodes that are added or removed during the process.
We found this issue during a stress test that repeatedly reads /sys/module directory to get a list of the currently loaded kernel modules while repeatedly loading and unloading kernel modules simultaneously.
v2: Fix the case where nodes with the same hash but with the name larger than the original node could still be skipped. Use kernfs_sd_compare() to compare kernfs_node objects. Imporove patch description.
Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com> Suggested-by: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com> Cc: Eric W. Biederman <ebiederm@aristanetworks.com> --- fs/kernfs/dir.c | 4 +++- 1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 89d1dc1..3aeeb7a 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1621,8 +1621,10 @@ static int kernfs_dir_fop_release(struct inode *inode, struct file *filp) static struct kernfs_node *kernfs_dir_next_pos(const void *ns, struct kernfs_node *parent, ino_t ino, struct kernfs_node *pos) { + struct kernfs_node *orig = pos; + pos = kernfs_dir_pos(ns, parent, ino, pos); - if (pos) { + if (pos && kernfs_sd_compare(pos, orig) <= 0) { do { struct rb_node *node = rb_next(&pos->rb); if (!node) -- 1.7.1
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