Messages in this thread | | | Date | Mon, 16 Aug 2010 13:21:24 -0700 | From | "Paul E. McKenney" <> | Subject | Re: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() usage (kernel/exit.c:1387) |
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On Mon, Aug 16, 2010 at 07:03:40PM +0200, Vegard Nossum wrote: > On the third try it will hopefully work. > > > Vegard > > ---------- Forwarded message ---------- > From: Vegard Nossum <vegard.nossum@gmail.com> > Date: 16 August 2010 19:01 > Subject: Re: 2.6.35+vfs-scale: INFO: suspicious > rcu_dereference_check() usage (kernel/exit.c:1387) > To: Nick Piggin <nickpiggin@yahoo.com.au> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, David Howells > <dhowells@redhat.com>, "Paul E. McKenney" > <paulmck@linux.vnet.ibm.com>, LKML <linux-kernel@vger.kernel.org> > > > Nick Piggin might update his git config because the commits in the > vfs-scale tree appear to bear an invalid e-mail address. Please reply > to this e-mail instead. Thanks. > > Vegard > > > ---------- Forwarded message ---------- > From: Vegard Nossum <vegard.nossum@gmail.com> > Date: 16 August 2010 18:57 > Subject: 2.6.35+vfs-scale: INFO: suspicious rcu_dereference_check() > usage (kernel/exit.c:1387) > To: Nick Piggin <npiggin@suse.de> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, David Howells > <dhowells@redhat.com>, "Paul E. McKenney" > <paulmck@linux.vnet.ibm.com>, LKML <linux-kernel@vger.kernel.org> > > > Hi, > > I was testing your VFS scaling tree*, but I get the following in my dmesg: > > =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > kernel/exit.c:1387 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 2 locks held by bash/2878: > #0: (tasklist_lock){.+.+..}, at: [<ffffffff8103a275>] do_wait+0xb3/0x200 > #1: (&(&sighand->siglock)->rlock){-.....}, at: [<ffffffff810399e9>] > wait_consider_task+0x2ca/0xaa3
Thank you for locating this!
OK, so we aren't holding rcu_read_lock(), nor is this task dead, so something needs some help.
We get from wait_consider_task() as follows: wait_consider_task() calls security_task_wait(), which calls either selinux_task_wait() or smack_task_wait(). Let's start with selinux_task_wait(), which calls task_has_perm(), which does a couple of __task_cred(), but does so under rcu_read_lock() protection, so presumably we didn't come in that way.
Dave, am I missing a code path somewhere here?
Thanx, Paul
> stack backtrace: > Pid: 2878, comm: bash Not tainted 2.6.35-00079-g4067b85 #7 > Call Trace: > [<ffffffff8105e9f2>] lockdep_rcu_dereference+0x9b/0xa6 > [<ffffffff8103a036>] wait_consider_task+0x917/0xaa3 > [<ffffffff8102cf36>] ? add_preempt_count+0xc2/0xc9 > [<ffffffff8103a29d>] do_wait+0xdb/0x200 > [<ffffffff8103a45b>] sys_wait4+0x99/0xd3 > [<ffffffff810387e5>] ? child_wait_callback+0x0/0x5d > [<ffffffff8109be66>] ? might_fault+0x96/0xbc > [<ffffffff810737a6>] compat_sys_wait4+0x8a/0xc1 > [<ffffffff8109be83>] ? might_fault+0xb3/0xbc > [<ffffffff8109be38>] ? might_fault+0x68/0xbc > [<ffffffff815d02c3>] ? trace_hardirqs_off_thunk+0x3a/0x3c > [<ffffffff8102862c>] sys32_waitpid+0xb/0xd > [<ffffffff81027bb4>] sysenter_dispatch+0x7/0x30 > [<ffffffff815d0284>] ? trace_hardirqs_on_thunk+0x3a/0x3f > > I don't think it's related to the VFS patches, however, so I added > some other (maybe relevant) CCs too. > > At the time I was simply invoking gcc from bash. > > > Vegard > > * git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin.git > branch vfs-scale -- 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/
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