• David Howells's avatar
    afs: Fix race in async call refcounting · 34fa4761
    David Howells authored
    There's a race between afs_make_call() and afs_wake_up_async_call() in the
    case that an error is returned from rxrpc_kernel_send_data() after it has
    queued the final packet.
    
    afs_make_call() will try and clean up the mess, but the call state may have
    been moved on thereby causing afs_process_async_call() to also try and to
    delete the call.
    
    Fix this by:
    
     (1) Getting an extra ref for an asynchronous call for the call itself to
         hold.  This makes sure the call doesn't evaporate on us accidentally
         and will allow the call to be retained by the caller in a future
         patch.  The ref is released on leaving afs_make_call() or
         afs_wait_for_call_to_complete().
    
     (2) In the event of an error from rxrpc_kernel_send_data():
    
         (a) Don't set the call state to AFS_CALL_COMPLETE until *after* the
         	 call has been aborted and ended.  This prevents
         	 afs_deliver_to_call() from doing anything with any notifications
         	 it gets.
    
         (b) Explicitly end the call immediately to prevent further callbacks.
    
         (c) Cancel any queued async_work and wait for the work if it's
         	 executing.  This allows us to be sure the race won't recur when we
         	 change the state.  We put the work queue's ref on the call if we
         	 managed to cancel it.
    
         (d) Put the call's ref that we got in (1).  This belongs to us as long
         	 as the call is in state AFS_CALL_CL_REQUESTING.
    
    Fixes: 341f741f ("afs: Refcount the afs_call struct")
    Signed-off-by: 's avatarDavid Howells <dhowells@redhat.com>
    34fa4761
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