Paul E. McKenney a écrit :
+/*
+ * Should we directly call rcu_do_batch() here ?
+ * if (unlikely(rdp->count > 10000))
+ * rcu_do_batch(rdp);
+ */
Good thing that the above is commented out! ;-)
Doing this can result in self-deadlock, for example with the following:
spin_lock(&mylock);
/* do some stuff. */
call_rcu(&p->rcu_head, my_rcu_callback);
/* do some more stuff. */
spin_unlock(&mylock);
void my_rcu_callback(struct rcu_head *p)
{
spin_lock(&mylock);
/* self-deadlock via call_rcu() via rcu_do_batch()!!! */
spin_unlock(&mylock);
}
Thanx, Paul
Thanks Paul for reminding us that call_rcu() should not ever call the callback
function, as very well documented in Documentation/RCU/UP.txt
(Example 3: Death by Deadlock)
But is the same true for call_rcu_bh() ?
I intentionally wrote the comment to remind readers that a low maxbatch can
trigger OOM in case a CPU is filled by some kind of DOS (network IRQ flood for
example, targeting the IP dst cache)
To solve this problem, may be we could add a requirement to
call_rcu_bh/callback functions : If they have to lock a spinlock, only use a
spin_trylock() and make them returns a status (0 : sucessfull callback, 1:
please requeue me)
As most callback functions just kfree() some memory, most of OOM would be cleared.
int my_rcu_callback(struct rcu_head *p)
{
if (!spin_trylock(&mylock))
return 1; /* please call me later */
/* do something here */
...
spin_unlock(&mylock);
return 0;
}
(Changes to rcu_do_batch() are left as an exercice :) )
Eric
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
