• David Howells's avatar
    afs: Fix hang on rmmod due to outstanding timer · 5481fc6e
    David Howells authored
    The fileserver probe timer, net->fs_probe_timer, isn't cancelled when
    the kafs module is being removed and so the count it holds on
    net->servers_outstanding doesn't get dropped..
    
    This causes rmmod to wait forever.  The hung process shows a stack like:
    
    	afs_purge_servers+0x1b5/0x23c [kafs]
    	afs_net_exit+0x44/0x6e [kafs]
    	ops_exit_list+0x72/0x93
    	unregister_pernet_operations+0x14c/0x1ba
    	unregister_pernet_subsys+0x1d/0x2a
    	afs_exit+0x29/0x6f [kafs]
    	__do_sys_delete_module.isra.0+0x1a2/0x24b
    	do_syscall_64+0x51/0x95
    	entry_SYSCALL_64_after_hwframe+0x44/0xa9
    
    Fix this by:
    
     (1) Attempting to cancel the probe timer and, if successful, drop the
         count that the timer was holding.
    
     (2) Make the timer function just drop the count and not schedule the
         prober if the afs portion of net namespace is being destroyed.
    
    Also, whilst we're at it, make the following changes:
    
     (3) Initialise net->servers_outstanding to 1 and decrement it before
         waiting on it so that it doesn't generate wake up events by being
         decremented to 0 until we're cleaning up.
    
     (4) Switch the atomic_dec() on ->servers_outstanding for ->fs_timer in
         afs_purge_servers() to use the helper function for that.
    
    Fixes: f6cbb368 ("afs: Actively poll fileservers to maintain NAT or firewall openings")
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    5481fc6e
main.c 6.35 KB