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    SubjectRe: [PATCH -tip 0/2] Temporary RCU fixes for notrace and hotplug CPU
    On Tue, Aug 25, 2009 at 12:25:49PM -0400, Mathieu Desnoyers wrote:
    > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
    > > On Tue, Aug 25, 2009 at 10:00:47AM +0200, Ingo Molnar wrote:
    > > >
    > > > btw., i'm still seeing crashes with the latest RCU bits:
    > > >
    > > > [ 20.621740] Testing event sys_enter_futex: OK
    > > > [ 20.629738] Testing event sys_exit_futex: OK
    > > > [ 20.637737] Testing event lock_acquire: [reboot]
    > > >
    > > > Possibly due to infinite recursion as well. Config attached.
    > >
    > > Color me confused...
    > >
    > > Unless someone has a better idea, I will send in a patch that adds
    > > "notrace" to every RCU API member used by any file in the kernel
    > > that has "trace" in its name (excluding ptrace.c and rcutree_trace.c,
    > > of course). This list is as follows:
    > >
    > > call_rcu()
    > > call_rcu_sched()
    > > rcu_read_lock()
    > > rcu_read_unlock()
    > >
    > > So, any better ideas?
    >
    > Tracers using RCU should use the _notrace() version of read_lock/unlock.
    > I think the callers should be fixed rather than RCU.
    >
    > Tracepoints have been designed to use the _notrace variant on the
    > instrumentation site. The core of tracepoint management use
    > call_rcu_sched(), which can be traced without any problem.
    >
    > I have not followed the late tracing development as closely though, so
    > errors might have crept in.

    Or I might have inadvertently broken something in a non-obvious (to me,
    anyway) manner.

    So, would you be willing to look at commit bc33f24bd in the -tip
    tree and see if there is anything I broke other than the now-fixed
    rcu_read_lock_sched_notrace() and rcu_read_unlock_sched_notrace()?
    And for that matter, whether my alleged fix for these two API members
    really does fix the problem (-tip commit 7c614d6461)?

    The -tip tree is at:

    git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git

    And these patches are on the tip/core/rcu branch.

    Thanx, Paul


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