Messages in this thread Patch in this message | | | Subject | Re: [PATCH] mce: fix RCU lockdep from mce_log() | From | Davidlohr Bueso <> | Date | Mon, 08 Nov 2010 08:30:19 -0300 |
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On Sun, 2010-11-07 at 05:39 -0800, Paul E. McKenney wrote: > 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))
this doesn't compile (mcelog.next is an index):
arch/x86/kernel/cpu/mcheck/mce.c: In function ‘mce_poll’: arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘_________p1’ arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘type name’ arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: cast to pointer from integer of different size arch/x86/kernel/cpu/mcheck/mce.c:1628: error: invalid type argument of ‘unary *’ (have ‘unsigned int’) arch/x86/kernel/cpu/mcheck/mce.c:1628: warning: type defaults to ‘int’ in declaration of ‘type name’ make[4]: *** [arch/x86/kernel/cpu/mcheck/mce.o] Error 1
Since the mutex is independent, what about this patch?
Signed-off-by: Davidlohr Bueso <dave@gnu.org>
--- arch/x86/kernel/cpu/mcheck/mce.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 7a35b72..cc1c673 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_dereference_index_check(mcelog.next, rcu_read_lock_sched_held())) return POLLIN | POLLRDNORM; if (!mce_apei_read_done && apei_check_mce()) return POLLIN | POLLRDNORM; -- 1.7.1
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