Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Sun, 7 Nov 2010 05:39:50 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] mce: fix RCU lockdep from mce_log() |
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On Sat, Nov 06, 2010 at 07:53:50PM +0100, Andi Kleen wrote: > On Fri, Nov 05, 2010 at 06:44:59PM -0300, Davidlohr Bueso wrote: > > Hi, > > > > Please review this patch, I am not very familiar with MCE/RCU so I'm not sure that this is the correct fix (otherwise consider it a bug report :)). > > This does "fix" the message though and I can use MCE normally. > > The patch is certainly not correct. The variable needs to be read > independently of the mutex.
This code is simply checking the value of the pointer, and therefore need not protect any actual dereferences. So why not replace the rcu_dereference_check_mce() with rcu_access_pointer()? If this is OK, please see the patch below.
BTW, assigning the value returned by rcu_access_pointer() into a variable often indicates a bug. ;-)
Thanx, Paul
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 7a35b72..4d29d50 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -1625,7 +1625,7 @@ out: static unsigned int mce_poll(struct file *file, poll_table *wait) { poll_wait(file, &mce_wait, wait); - if (rcu_dereference_check_mce(mcelog.next)) + if (rcu_access_pointer(mcelog.next)) return POLLIN | POLLRDNORM; if (!mce_apei_read_done && apei_check_mce()) return POLLIN | POLLRDNORM;
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