[2637] | 1 | From c9bbebe869acadd61abfa50656447429cde18aaf Mon Sep 17 00:00:00 2001 |
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| 2 | From: Andrew Deason <adeason@sinenomine.net> |
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| 3 | Date: Tue, 28 Oct 2014 00:10:56 -0500 |
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| 4 | Subject: [PATCH] LINUX: Avoid d_revalidate failure on mtpt mismatch |
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| 5 | |
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| 6 | Currently, if afs_linux_dentry_revalidate is given an inode that |
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| 7 | corresponds to a mtpt vcache ('vcp'), it resolves the mtpt to its root |
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| 8 | dir if it's easy to do so (mvid and CMValid are set). Later on, we run |
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| 9 | afs_lookup to see if looking up our dentry's name returns the same |
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| 10 | vcache that we got; afs_lookup presumably will also resolve the mtpt |
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| 11 | if it's easy to do so. |
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| 12 | |
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| 13 | However, it is possible that afs_linux_dentry_revalidate and |
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| 14 | afs_lookup will make different decisions as to whether or not they |
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| 15 | resolve a mtpt to a dir. Specifically, if CMValid is cleared after |
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| 16 | afs_linux_dentry_revalidate checks for it, but before afs_lookup does, |
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| 17 | then afs_lookup will return a different vcache than |
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| 18 | afs_linux_dentry_revalidate is expecting, even though the relevant |
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| 19 | directory entry has not changed. That is, tvc is not equal to vcp, but |
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| 20 | tvc could be a mtpt that resolves to vcp, or vice versa. CMValid can |
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| 21 | be cleared by another thread at virtually any time, since this is |
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| 22 | cleared in some situations when we're not sure if the mtpt resolution |
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| 23 | is still valid (callbacks are broken, vldb cache entries expire, etc). |
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| 24 | |
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| 25 | afs_linux_dentry_revalidate interprets this situation to mean that the |
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| 26 | directory entry has changed, and so it eventually d_drop's the |
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| 27 | associated dentry. The way that this manifests to users is that a |
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| 28 | "fakestatted" mtpt can appear to be deleted effectively randomly, even |
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| 29 | when nothing has changed. This can be a problem because this causes |
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| 30 | the getcwd() syscall to return ENOENT when the working directory |
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| 31 | involves such an affected directory. |
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| 32 | |
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| 33 | To fix this situation, we just detect if afs_lookup returned either |
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| 34 | 'vcp' (our possibly-resolved vcache), or the original inode associated |
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| 35 | with the dentry we are revalidating. If the returned vcache matches |
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| 36 | either of these, then the entry is okay and we don't need to |
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| 37 | invalidate or drop anything. |
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| 38 | |
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| 39 | FIXES 131780 |
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| 40 | |
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| 41 | Change-Id: Ide1dd224d1ea1e29a82eb7130a010877cf4e9fc7 |
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| 42 | (cherry picked from commit 45d9ff86571cbe70fedd524266fac50bd2d4bc2d) |
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| 43 | --- |
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| 44 | src/afs/LINUX/osi_vnodeops.c | 29 ++++++++++++++++++++++++++++- |
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| 45 | 1 file changed, 28 insertions(+), 1 deletion(-) |
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| 46 | |
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| 47 | diff --git a/src/afs/LINUX/osi_vnodeops.c b/src/afs/LINUX/osi_vnodeops.c |
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| 48 | index 9ed6f01..8c63f96 100644 |
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| 49 | --- a/src/afs/LINUX/osi_vnodeops.c |
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| 50 | +++ b/src/afs/LINUX/osi_vnodeops.c |
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| 51 | @@ -1231,10 +1231,37 @@ afs_linux_dentry_revalidate(struct dentry *dp, int flags) |
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| 52 | if (hgetlo(pvcp->f.m.DataVersion) > dp->d_time || !(vcp->f.states & CStatd)) { |
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| 53 | struct vattr *vattr = NULL; |
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| 54 | int code; |
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| 55 | + int lookup_good; |
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| 56 | |
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| 57 | credp = crref(); |
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| 58 | code = afs_lookup(pvcp, (char *)dp->d_name.name, &tvc, credp); |
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| 59 | - if (code || tvc != vcp) { |
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| 60 | + |
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| 61 | + if (code) { |
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| 62 | + /* We couldn't perform the lookup, so we're not okay. */ |
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| 63 | + lookup_good = 0; |
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| 64 | + |
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| 65 | + } else if (tvc == vcp) { |
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| 66 | + /* We got back the same vcache, so we're good. */ |
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| 67 | + lookup_good = 1; |
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| 68 | + |
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| 69 | + } else if (tvc == VTOAFS(dp->d_inode)) { |
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| 70 | + /* We got back the same vcache, so we're good. This is |
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| 71 | + * different from the above case, because sometimes 'vcp' is |
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| 72 | + * not the same as the vcache for dp->d_inode, if 'vcp' was a |
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| 73 | + * mtpt and we evaluated it to a root dir. In rare cases, |
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| 74 | + * afs_lookup might not evalute the mtpt when we do, or vice |
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| 75 | + * versa, so the previous case will not succeed. But this is |
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| 76 | + * still 'correct', so make sure not to mark the dentry as |
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| 77 | + * invalid; it still points to the same thing! */ |
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| 78 | + lookup_good = 1; |
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| 79 | + |
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| 80 | + } else { |
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| 81 | + /* We got back a different file, so we're definitely not |
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| 82 | + * okay. */ |
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| 83 | + lookup_good = 0; |
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| 84 | + } |
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| 85 | + |
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| 86 | + if (!lookup_good) { |
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| 87 | dput(parent); |
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| 88 | /* Force unhash; the name doesn't point to this file |
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| 89 | * anymore. */ |
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| 90 | -- |
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| 91 | 2.1.2 |
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| 92 | |
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