From: Dave Wysochanski dwysocha@redhat.com
[ Upstream commit d9bfced1fbcb35b28d8fbed4e785d2807055ed2b ]
Commit 402cb8dda949 ("fscache: Attach the index key and aux data to the cookie") added the index_key and index_key_len parameters to fscache_acquire_cookie(), and updated the callers in the NFS client. One of the callers was inside nfs_fscache_get_super_cookie() and was changed to use the full struct nfs_fscache_key as the index_key. However, a couple members of this structure contain pointers and thus will change each time the same NFS share is remounted. Since index_key is used for fscache_cookie->key_hash and this subsequently is used to compare cookies, the effectiveness of fscache with NFS is reduced to the point at which a umount occurs. Any subsequent remount of the same share will cause a unique NFS super_block index_key and key_hash to be generated for the same data, rendering any prior fscache data unable to be found. A simple reproducer demonstrates the problem.
1. Mount share with 'fsc', create a file, drop page cache systemctl start cachefilesd mount -o vers=3,fsc 127.0.0.1:/export /mnt dd if=/dev/zero of=/mnt/file1.bin bs=4096 count=1 echo 3 > /proc/sys/vm/drop_caches
2. Read file into page cache and fscache, then unmount dd if=/mnt/file1.bin of=/dev/null bs=4096 count=1 umount /mnt
3. Remount and re-read which should come from fscache mount -o vers=3,fsc 127.0.0.1:/export /mnt echo 3 > /proc/sys/vm/drop_caches dd if=/mnt/file1.bin of=/dev/null bs=4096 count=1
4. Check for READ ops in mountstats - there should be none grep READ: /proc/self/mountstats
Looking at the history and the removed function, nfs_super_get_key(), we should only use nfs_fscache_key.key plus any uniquifier, for the fscache index_key.
Fixes: 402cb8dda949 ("fscache: Attach the index key and aux data to the cookie") Signed-off-by: Dave Wysochanski dwysocha@redhat.com Signed-off-by: David Howells dhowells@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/nfs/fscache.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c index 6f45b1a..b931169 100644 --- a/fs/nfs/fscache.c +++ b/fs/nfs/fscache.c @@ -192,7 +192,8 @@ void nfs_fscache_get_super_cookie(struct super_block *sb, const char *uniq, int /* create a cache index for looking up filehandles */ nfss->fscache = fscache_acquire_cookie(nfss->nfs_client->fscache, &nfs_fscache_super_index_def, - key, sizeof(*key) + ulen, + &key->key, + sizeof(key->key) + ulen, NULL, 0, nfss, 0, true); dfprintk(FSCACHE, "NFS: get superblock cookie (0x%p/0x%p)\n",