lkml.org 
[lkml]   [2010]   [Nov]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] mce: fix RCU lockdep from mce_log()
    On Mon, Nov 08, 2010 at 08:30:19AM -0300, Davidlohr Bueso wrote:
    > 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?

    Looks good to me!

    Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    > 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
    >
    >
    >
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2010-11-08 14:19    [W:0.026 / U:216.708 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site