afs: Avoid afs_GetDCache panic on cache open error

When we need to populate a dcache entry, afs_GetDCache calls
afs_CFileOpen to get a handle for our file backing that dcache.
Currently, if we cannot open the file, we panic.

To handle this a little more gracefully, just return an error from
afs_GetDCache instead. The relevant userspace request will probably
fail with EIO, but this is better than possibly crashing the whole
system.

Reviewed-on: https://gerrit.openafs.org/13046
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 22e64df8e043fa7bd78bff263866ee2bd6a6e13d)

Change-Id: Iddc7b0ebc56a64d792251f1f42c576603f2a86cf
Reviewed-on: https://gerrit.openafs.org/13072
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>

diff --git a/src/afs/afs_dcache.c b/src/afs/afs_dcache.c
index 321e37f5ac43e8ea0bc61abff535409bf2bab248..6ca9c1fa1d7ac34342a7371e71ef1c007cc5eff0 100644 (file)
--- a/src/afs/afs_dcache.c
+++ b/src/afs/afs_dcache.c
@@ -2298,7 +2298,14 @@ afs_GetDCache(struct vcache *avc, afs_size_t abyte,
         */
        DZap(tdc);      /* pages in cache may be old */
        file = afs_CFileOpen(&tdc->f.inode);
-        osi_Assert(file);
+        if (!file) {
+            /* We can't access the file in the disk cache backing this dcache;
+             * bail out. */
+            ReleaseWriteLock(&tdc->lock);
+            afs_PutDCache(tdc);
+            tdc = NULL;
+            goto done;
+        }
        afs_RemoveVCB(&avc->f.fid);
        tdc->f.states |= DWriting;
        tdc->dflags |= DFFetching;