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    SubjectRe: [Bug #10815] 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
    On Sat, Jun 14, 2008 at 08:30:01PM -0700, Paul E. McKenney wrote:
    > On Sat, Jun 14, 2008 at 11:43:38PM +0400, Alexey Dobriyan wrote:
    > > On Sat, Jun 14, 2008 at 11:12:12AM -0700, Paul E. McKenney wrote:
    > > > On Sat, Jun 14, 2008 at 06:58:39PM +0400, Oleg Nesterov wrote:
    > > > > On 06/14, Paul E. McKenney wrote:
    > > > > >
    > > > > > On Fri, Jun 13, 2008 at 04:52:55PM +0300, Adrian Bunk wrote:
    > > > > > > On Sat, Jun 07, 2008 at 10:42:57PM +0200, Rafael J. Wysocki wrote:
    > > > > > > > This message has been generated automatically as a part of a report
    > > > > > > > of recent regressions.
    > > > > > > >
    > > > > > > > The following bug entry is on the current list of known regressions
    > > > > > > > from 2.6.25. Please verify if it still should be listed.
    > > > > > > >
    > > > > > > >
    > > > > > > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=10815
    > > > > > > > Subject : 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
    > > > > > > > Submitter : Alexey Dobriyan <adobriyan@gmail.com>
    > > > > > > > Date : 2008-05-27 09:23 (12 days old)
    > > > > > > > References : http://lkml.org/lkml/2008/5/27/9
    > > > > > > > Handled-By : Oleg Nesterov <oleg@tv-sign.ru>
    > > > > > > > Linus Torvalds <torvalds@linux-foundation.org>
    > > > > > > > Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > > > > > > > Patch : http://lkml.org/lkml/2008/5/28/16
    > > > > > >
    > > > > > > What happened with this issue?
    > > > > >
    > > > > > The patch listed above works for me, passes rcutorture, &c. However,
    > > > > > I never have been able to reproduce the original problem, so cannot say
    > > > > > whether it qualifies as a fix.
    > > > >
    > > > > I doubt very much RCU was the reason of this problem.
    > > >
    > > > Although I very much appreciate your confidence in my code, it is new
    > > > code, so therefore under suspicion.
    > > >
    > > > > Alexey, how did you trigger this problem?
    > > >
    > > > One of them involved running LTP while doing 170 kernel builds in
    > > > parallel.
    > >
    > > My gut feeling is that find_pid_ns oops, __d_lookup oops and
    > > __call_for_each_cic oops are the same bug.
    > >
    > > And rcutorture failures I've mentioned to Paul privately.
    >
    > Yep, running rcutorture in parallel with LTP, which didn't reproduce
    > for me either.
    >
    > Did the patch at http://lkml.org/lkml/2008/5/28/16 help?
    >
    > > Oleg, debugging you've posted never triggered.
    > >
    > > kerneloops suggests that I'm alone. :-(
    >
    > Assuming that the above patch didn't help... As a desperation measure,
    > I could suggest the following patch.

    > --- linux-2.6.26-rc4/kernel/rcupreempt.c
    > +++ linux-2.6.26-rc4-alexey/kernel/rcupreempt.c
    > @@ -77,7 +77,7 @@
    > *
    > * GP in GP_STAGES stands for Grace Period ;)
    > */
    > -#define GP_STAGES 2
    > +#define GP_STAGES 3
    > struct rcu_data {
    > spinlock_t lock; /* Protect rcu_data fields. */
    > long completed; /* Number of last completed batch. */

    Both patches (independently) do not help with rcutortures failures:

    [ 58.968404] rcu-torture:--- Start of test: nreaders=4 nfakewriters=4 stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval = 5
    [ 159.044524] rcu-torture: rtc: 0000000000000000 ver: 53859 tfle: 0 rta: 53859 rtaf: 18 rtf: 53797 rtmbe: 0
    [ 159.044527] rcu-torture: !!! Reader Pipe: 65565142 4275 1 0 0 0 0 0 0 0 0
    [ 159.044529] rcu-torture: Reader Batch: 65564196 5207 7 3 1 1 0 1 1 0 1
    [ 159.044530] rcu-torture: Free-Block Circulation: 53858 53853 53846 53843 53834 53825 53816 53808 53803 53797 0
    [ 159.044976] rcu-torture:--- End of test: FAILURE: nreaders=4 nfakewriters=4 stat_interval=0 verbose=0 test_no_idle_hz=0 shuffle_interval = 5



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