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| /freebsd-10.2-release/sys/kern/ | ||
| H A D | vfs_cache.c | diff 182061 Sat Aug 23 15:15:26 MDT 2008 jhb Fix a race condition with concurrent LOOKUP namecache operations for a vnode not in the namecache when shared lookups are enabled (vfs.lookup_shared=1, it is currently off by default) and the filesystem supports shared lookups (e.g. NFS client). Specifically, if multiple concurrent LOOKUPs both miss in the name cache in parallel, each of the lookups may each end up adding an entry to the namecache resulting in duplicate entries in the namecache for the same pathname. A subsequent removal of the mapping of that pathname to that vnode (via remove or rename) would only evict one of the entries from the name cache. As a result, subseqent lookups for that pathname would still return the old vnode. This race was observed with shared lookups over NFS where a file was updated by writing a new file out to a temporary file name and then renaming that temporary file to the "real" file to effect atomic updates of a file. Other processes on the same client that were periodically reading the file would occasionally receive an ESTALE error from open(2) because the VOP_GETATTR() in nfs_open() would receive that error when given the stale vnode. The fix here is to check for duplicates in cache_enter() and just return if an entry for this same directory and leaf file name for this vnode is already in the cache. The check for duplicates is done by walking the per-vnode list of name cache entries. It is expected that this list should be very small in the common case (usually 0 or 1 entries during a cache_enter() since most files only have 1 "leaf" name). Reviewed by: ups, scottl MFC after: 2 months |
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