I am having the same problem on ubuntu 16.04.2, kernel 4.4.0-75-generic, and on a mint 18 system, kernel 4.4.0-21-generic. I have several cifs mounts, and if any one server becomes unresponsive, then any process attempting to access the mounts will hang indefinitely. If I unmount using -l and wait several minutes, eventually these hung processes will resume (with an error). I am mounting with the "soft" option.
I am having the same problem on ubuntu 16.04.2, kernel 4.4.0-75-generic, and on a mint 18 system, kernel 4.4.0-21-generic. I have several cifs mounts, and if any one server becomes unresponsive, then any process attempting to access the mounts will hang indefinitely. If I unmount using -l and wait several minutes, eventually these hung processes will resume (with an error). I am mounting with the "soft" option.
The hung process stack looks like: 70d>] cifs_reconnect_ tcon+0x9d/ 0x340 [cifs] a5a>] smb_init+0x2a/0x50 [cifs] c53>] CIFSSMBQPathInf o+0x63/ 0x2e0 [cifs] 20f>] cifs_query_ path_info+ 0x6f/0x1a0 [cifs] e80>] cifs_get_ inode_info+ 0x390/0x8f0 [cifs] 425>] cifs_revalidate _dentry_ attr+0x1d5/ 0x250 [cifs] 551>] cifs_getattr+ 0x51/0x110 [cifs] a6c>] vfs_getattr_ nosec+0x2c/ 0x40 c86>] vfs_getattr+ 0x26/0x30 d68>] vfs_fstatat+ 0x78/0xc0 311>] SYSC_newlstat+ 0x31/0x60 44e>] SyS_newlstat+ 0xe/0x10 972>] entry_SYSCALL_ 64_fastpath+ 0x16/0x71 fff>] 0xffffffffffffffff
$ sudo cat /proc/7771/stack
[<ffffffffc0309
[<ffffffffc0309
[<ffffffffc0310
[<ffffffffc033c
[<ffffffffc032a
[<ffffffffc032d
[<ffffffffc032d
[<ffffffff81213
[<ffffffff81213
[<ffffffff81213
[<ffffffff81214
[<ffffffff81214
[<ffffffff8183b
[<fffffffffffff