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    SubjectRe: [tip:core/rcu] rcu: Consolidate sparse and lockdep declarations in include/linux/rcupdate.h
    On Mon, Aug 24, 2009 at 11:28:36AM +0200, Ingo Molnar wrote:
    >
    > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
    >
    > > On Sun, Aug 23, 2009 at 12:33:56PM -0700, Paul E. McKenney wrote:
    > > > On Sun, Aug 23, 2009 at 08:42:02PM +0200, Ingo Molnar wrote:
    > > > >
    > > > > * tip-bot for Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
    > > > >
    > > > > > Commit-ID: bc33f24bdca8b6e97376e3a182ab69e6cdefa989
    > > > > > Gitweb: http://git.kernel.org/tip/bc33f24bdca8b6e97376e3a182ab69e6cdefa989
    > > > > > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > > > > > AuthorDate: Sat, 22 Aug 2009 13:56:47 -0700
    > > > > > Committer: Ingo Molnar <mingo@elte.hu>
    > > > > > CommitDate: Sun, 23 Aug 2009 10:32:37 +0200
    > > > > >
    > > > > > rcu: Consolidate sparse and lockdep declarations in include/linux/rcupdate.h
    > > > >
    > > > > -tip testing found a spontaneous reboot crash, which i
    > > > > bisected back to this commit:
    > > > >
    > > > > bc33f24bdca8b6e97376e3a182ab69e6cdefa989 is first bad commit
    > > > >
    > > > > the reboot happens during the ftrace syscall tracepoints
    > > > > self-test:
    > > > >
    > > > > [ 34.618832] Testing event sys_exit_set_robust_list: OK
    > > > > [ 34.635511] Testing event sys_enter_get_robust_list: OK
    > > > > [ 34.652164] Testing event sys_exit_get_robust_list: OK
    > > > > [ 34.668844] Testing event sys_enter_futex: OK
    > > > > [ 34.685495] Testing event sys_exit_futex: OK
    > > > > [ 34.702170] Testing event lock_acquire: [instant reboot]
    > > > >
    > > > > There's no log message - just a reboot - which signals some
    > > > > severe crash - perhaps some locking related infinite
    > > > > recursion or something like that?
    > > >
    > > > Pretty impressive for having mostly moved RCU's lockdep-related
    > > > declarations from one file to another... :-/
    > > >
    > > > Looking into it, probably a typo on my part.
    > >
    > > I rechecked this several times, and don't see how anything else
    > > should have noticed this patch. That said, that self-test is
    > > rather amazing code, so...
    >
    > What do you think about the infinite recursion bug that Lai
    > Jiangshan's found in that patch? (sharp eyes really!) That might
    > explain the crash -tip testing found.

    Indeed!!!

    My thought is to send you a temporary patch stack fixing that bug
    (and supplying a CPU-hotplug fix), allowing your testing to progress
    (but defeating bisection if using ftrace).

    Then I would create a new patch stack applying the fix to the bugs Lai
    Jiangshan found to commit bc33f24, rebasing, retesting, and suppling a
    this new stack to replace commit bc33f24 and later in tip/core/rcu.

    Seem reasonable?

    Thanx, Paul


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