Jarek Poplawski wrote:
On 18-09-2007 16:55, Nadia Derbey wrote:
...
Well, reviewing the code I found another place where the
rcu_read_unlock() was missing.
I'm so sorry for the inconvenience. It's true that I should have tested
with CONFIG_PREEMPT=y :-(
Now, the ltp tests pass even with this option set...
In attachment you'll find a patch thhat
1) adds the missing rcu_read_unlock()
2) replaces Andrew's fix with a new one: the rcu_read_lock() is now
taken in ipc_lock() / ipc_lock_by_ptr() and released in ipc_unlock(),
exactly as it was done in the ref code.
BTW, probably I miss something, but I wonder, how this RCU is working
here. E.g. in msg.c do_msgsnd() there is:
msq = msg_lock_check(ns, msqid);
...
msg_unlock(msq);
schedule();
ipc_lock_by_ptr(&msq->q_perm);
Since msq_lock_check() gets msq with ipc_lock_check() under
rcu_read_lock(), and then goes msg_unlock(msq) (i.e. ipc_unlock())
with rcu_read_unlock(), is it valid to use this with
ipc_lock_by_ptr() yet?
Before Calling msg_unlock() they call ipc_rcu_getref() that increments a
refcount in the rcu header for the msg structure. This guarantees that
the the structure won't be freed before they relock it. Once the
structure is relocked by ipc_lock_by_ptr(), they do the symmetric
operation i.e. ipc_rcu_putref().
Regards,
Nadia
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