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rcu: Make call_rcu() leak callbacks for debug-object errors

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If someone does a duplicate call_rcu(), the worst thing the second
call_rcu() could do would be to actually queue the callback the second
time because doing so corrupts whatever list the callback was already
queued on.  This commit therefore makes __call_rcu() check the new
return value from debug-objects and leak the callback upon error.
This commit also substitutes rcu_leak_callback() for whatever callback
function was previously in place in order to avoid freeing the callback
out from under any readers that might still be referencing it.

These changes increase the probability that the debug-objects error
messages will actually make it somewhere visible.

Signed-off-by: Paul E. McKenney <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Sedat Dilek <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Linus Torvalds <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Reviewed-by: Josh Triplett <[email protected]>
This commit is contained in:
Paul E. McKenney 2013-04-23 13:20:57 -07:00
commit ae15018456
2 changed files with 20 additions and 4 deletions
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14
kernel/rcutree.c
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@ -2304,6 +2304,13 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
}
}
/*
* RCU callback function to leak a callback.
*/
static void rcu_leak_callback(struct rcu_head *rhp)
{
}
/*
* Helper function for call_rcu() and friends. The cpu argument will
* normally be -1, indicating "currently running CPU". It may specify
@ -2318,7 +2325,12 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_data *rdp;
WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
debug_rcu_head_queue(head);
if (debug_rcu_head_queue(head)) {
/* Probable double call_rcu(), so leak the callback. */
ACCESS_ONCE(head->func) = rcu_leak_callback;
WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
return;
}
head->func = func;
head->next = NULL;