From c9bbebe869acadd61abfa50656447429cde18aaf 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 (cherry picked from commit 45d9ff86571cbe70fedd524266fac50bd2d4bc2d) --- 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 9ed6f01..8c63f96 100644 --- a/src/afs/LINUX/osi_vnodeops.c +++ b/src/afs/LINUX/osi_vnodeops.c @@ -1231,10 +1231,37 @@ afs_linux_dentry_revalidate(struct dentry *dp, int flags) if (hgetlo(pvcp->f.m.DataVersion) > dp->d_time || !(vcp->f.states & CStatd)) { struct vattr *vattr = NULL; int code; + int lookup_good; credp = crref(); 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. */ -- 2.1.2