From ba1cc838ab4a80b7a7787c441a79aca31d84808c Mon Sep 17 00:00:00 2001 From: Andrew Deason Date: Tue, 28 Oct 2014 00:10:56 -0500 Subject: [PATCH] LINUX: Avoid d_revalidate failure on mtpt mismatch Currently, if afs_linux_dentry_revalidate is given an inode that corresponds to a mtpt vcache ('vcp'), it resolves the mtpt to its root dir if it's easy to do so (mvid and CMValid are set). Later on, we run afs_lookup to see if looking up our dentry's name returns the same vcache that we got; afs_lookup presumably will also resolve the mtpt if it's easy to do so. However, it is possible that afs_linux_dentry_revalidate and afs_lookup will make different decisions as to whether or not they resolve a mtpt to a dir. Specifically, if CMValid is cleared after afs_linux_dentry_revalidate checks for it, but before afs_lookup does, then afs_lookup will return a different vcache than afs_linux_dentry_revalidate is expecting, even though the relevant directory entry has not changed. That is, tvc is not equal to vcp, but tvc could be a mtpt that resolves to vcp, or vice versa. CMValid can be cleared by another thread at virtually any time, since this is cleared in some situations when we're not sure if the mtpt resolution is still valid (callbacks are broken, vldb cache entries expire, etc). afs_linux_dentry_revalidate interprets this situation to mean that the directory entry has changed, and so it eventually d_drop's the associated dentry. The way that this manifests to users is that a "fakestatted" mtpt can appear to be deleted effectively randomly, even when nothing has changed. This can be a problem because this causes the getcwd() syscall to return ENOENT when the working directory involves such an affected directory. To fix this situation, we just detect if afs_lookup returned either 'vcp' (our possibly-resolved vcache), or the original inode associated with the dentry we are revalidating. If the returned vcache matches either of these, then the entry is okay and we don't need to invalidate or drop anything. FIXES 131780 Change-Id: Ide1dd224d1ea1e29a82eb7130a010877cf4e9fc7 Reviewed-on: http://gerrit.openafs.org/11559 Tested-by: BuildBot Reviewed-by: Benjamin Kaduk Tested-by: Anders Kaseorg Reviewed-by: Anders Kaseorg Reviewed-by: D Brashear --- src/afs/LINUX/osi_vnodeops.c | 29 ++++++++++++++++++++++++++++- 1 file changed, 28 insertions(+), 1 deletion(-) diff --git a/src/afs/LINUX/osi_vnodeops.c b/src/afs/LINUX/osi_vnodeops.c index 0cdd9e0d1a..b2ab9d53e3 100644 --- a/src/afs/LINUX/osi_vnodeops.c +++ b/src/afs/LINUX/osi_vnodeops.c @@ -1291,9 +1291,36 @@ afs_linux_dentry_revalidate(struct dentry *dp, int flags) if (locked && (parent_dv > dp->d_time || !(vcp->f.states & CStatd))) { struct vattr *vattr = NULL; int code; + int lookup_good; code = afs_lookup(pvcp, (char *)dp->d_name.name, &tvc, credp); - if (code || tvc != vcp) { + + if (code) { + /* We couldn't perform the lookup, so we're not okay. */ + lookup_good = 0; + + } else if (tvc == vcp) { + /* We got back the same vcache, so we're good. */ + lookup_good = 1; + + } else if (tvc == VTOAFS(dp->d_inode)) { + /* We got back the same vcache, so we're good. This is + * different from the above case, because sometimes 'vcp' is + * not the same as the vcache for dp->d_inode, if 'vcp' was a + * mtpt and we evaluated it to a root dir. In rare cases, + * afs_lookup might not evalute the mtpt when we do, or vice + * versa, so the previous case will not succeed. But this is + * still 'correct', so make sure not to mark the dentry as + * invalid; it still points to the same thing! */ + lookup_good = 1; + + } else { + /* We got back a different file, so we're definitely not + * okay. */ + lookup_good = 0; + } + + if (!lookup_good) { dput(parent); /* Force unhash; the name doesn't point to this file * anymore. */