On 03/18/2013 04:32 PM, Neil Horman wrote:
On Mon, Mar 18, 2013 at 11:31:06AM -0400, Vlad Yasevich wrote:
On 03/18/2013 11:25 AM, Eric Dumazet wrote:
On Mon, 2013-03-18 at 07:04 -0400, Neil Horman wrote:
I'm not sure why the process would never get back to the schedule, but looking
at the sctp_remaddr_seq_show function, I think that we should convert this
sequence:
sctp_local_bh_disable();
read_lock(&head->lock);
rcu_read_lock();
to this:
read_lock(&head->lock);
rcu_read_lock_bh();
Neil
I dont think so.
BH needs to be disabled before read_lock(&head->lock);
or else, write_lock() could deadlock (assuming it can be called from BH)
If anything, this should probably be done like this:
rcu_read_lock();
read_lock_bh(&head->lock)
...
read_unlock_bh(&head->lock)
rcu_read_unlock();
Vlads, right. We need to grab the rcu lock before the read lock, but we should
probably use the rcu_read_lock_bh variant, since we're going to disable bottom
halves anyway.
I don't think disabling bh as part of rcu gains us anything. The main
thing that has to happen is that it needs to be disabled before the hash
read_lock(). Doing it my way means that we wouldn't have to touch
call_rcu() sites. If we change to rcu_read_lock_bh(), we could have to
convert to call_rcu_bh() and still wouldn't see any gain.
In any case, this is all completely theoretical as the code the way it
is now should still work and not hang in bh_enable.
Sasha, if you can trigger it easily enough, could you try the above
alternatives.
Thanks
-vlad
Neil
-vlad
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