• Peter Zijlstra's avatar
    notifier: Fix broken error handling pattern · 70d93298
    Peter Zijlstra authored
    The current notifiers have the following error handling pattern all
    over the place:
    
    	int err, nr;
    
    	err = __foo_notifier_call_chain(&chain, val_up, v, -1, &nr);
    	if (err & NOTIFIER_STOP_MASK)
    		__foo_notifier_call_chain(&chain, val_down, v, nr-1, NULL)
    
    And aside from the endless repetition thereof, it is broken. Consider
    blocking notifiers; both calls take and drop the rwsem, this means
    that the notifier list can change in between the two calls, making @nr
    meaningless.
    
    Fix this by replacing all the __foo_notifier_call_chain() functions
    with foo_notifier_call_chain_robust() that embeds the above pattern,
    but ensures it is inside a single lock region.
    
    Note: I switched atomic_notifier_call_chain_robust() to use
          the spinlock, since RCU cannot provide the guarantee
          required for the recovery.
    
    Note: software_resume() error handling was broken afaict.
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Acked-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Link: https://lore.kernel.org/r/20200818135804.325626653@infradead.org
    70d93298
user.c 9.57 KB