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SubjectRe: mmotm 2010-04-05 - another RCU whinge (not network this time)
On Thu, Apr 08, 2010 at 07:57:28PM -0400, Valdis.Kletnieks@vt.edu wrote:
> On Mon, 05 Apr 2010 16:09:45 PDT, akpm@linux-foundation.org said:
> > The mm-of-the-moment snapshot 2010-04-05-16-09 has been uploaded to
> >
> > http://userweb.kernel.org/~akpm/mmotm/
>
> Hit another one. I seem to be on a roll...
>
> Seen in dmesg, happened near end of the initrd..
>
> [ 26.756864]
> [ 26.756866] ===================================================
> [ 26.756869] [ INFO: suspicious rcu_dereference_check() usage. ]
> [ 26.756871] ---------------------------------------------------
> [ 26.756874] fs/proc/array.c:241 invoked rcu_dereference_check() without protection!

Color me confused. I cloned James Toy's git repository at
git://zen-kernel.org/kernel/mmotm.git, and gitk claims that I am on tag
2010-04-05-16-09, which matches the string above. But when I look at
fs/proc/array.c near line 241, I see:

238 static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
239 sigset_t *catch)
240 {
241 struct k_sigaction *k;
242 int i;
243
244 k = p->sighand->action;
245 for (i = 1; i <= _NSIG; ++i, ++k) {
246 if (k->sa.sa_handler == SIG_IGN)
247 sigaddset(ign, i);
248 else if (k->sa.sa_handler != SIG_DFL)
249 sigaddset(catch, i);
250 }
251 }

It seems unlikely that line 241 generated the above error.

Am I on the wrong version? Or do the git tags not mean what I think
that they mean?

Thanx, Paul

> [ 26.756876]
> [ 26.756877] other info that might help us debug this:
> [ 26.756877]
> [ 26.756879]
> [ 26.756880] rcu_scheduler_active = 1, debug_locks = 0
> [ 26.756883] 2 locks held by pidof/2197:
> [ 26.756884] #0: (&p->lock){+.+.+.}, at: [<ffffffff810f4c2a>] seq_read+0x3a/0x42d
> [ 26.756894] #1: (&(&sighand->siglock)->rlock){......}, at: [<ffffffff81047eff>] lock_task_sighand+0x79/0xcf
> [ 26.756903]
> [ 26.756903] stack backtrace:
> [ 26.756906] Pid: 2197, comm: pidof Not tainted 2.6.34-rc3-mmotm0405 #3
> [ 26.756909] Call Trace:
> [ 26.756914] [<ffffffff810638c5>] lockdep_rcu_dereference+0xaa/0xb2
> [ 26.756919] [<ffffffff8112ed88>] collect_sigign_sigcatch+0x37/0xa0
> [ 26.756923] [<ffffffff8112f066>] do_task_stat+0x275/0x837
> [ 26.756927] [<ffffffff81063f83>] ? mark_held_locks+0x52/0x70
> [ 26.756931] [<ffffffff810af6be>] ? get_page_from_freelist+0x390/0x5ab
> [ 26.756935] [<ffffffff81062e7b>] ? register_lock_class+0x1e/0x325
> [ 26.756938] [<ffffffff8106421a>] ? trace_hardirqs_on+0xd/0xf
> [ 26.756942] [<ffffffff810af742>] ? get_page_from_freelist+0x414/0x5ab
> [ 26.756946] [<ffffffff81063d32>] ? mark_lock+0x2d/0x22c
> [ 26.756949] [<ffffffff81063d32>] ? mark_lock+0x2d/0x22c
> [ 26.756953] [<ffffffff81064fe7>] ? __lock_acquire+0x391/0xcfc
> [ 26.756956] [<ffffffff810b006f>] ? __alloc_pages_nodemask+0x796/0x823
> [ 26.756961] [<ffffffff810d4e60>] ? ____cache_alloc+0x10a/0x5cb
> [ 26.756964] [<ffffffff810d4e60>] ? ____cache_alloc+0x10a/0x5cb
> [ 26.756969] [<ffffffff8159f84c>] ? sub_preempt_count+0x35/0x49
> [ 26.756973] [<ffffffff8112f637>] proc_tgid_stat+0xf/0x11
> [ 26.756977] [<ffffffff8112c005>] proc_single_show+0x57/0x74
> [ 26.756980] [<ffffffff810f4ca1>] ? seq_read+0xb1/0x42d
> [ 26.756983] [<ffffffff810f4dc3>] seq_read+0x1d3/0x42d
> [ 26.756988] [<ffffffff810da357>] vfs_read+0xe0/0x140
> [ 26.756991] [<ffffffff810da46d>] sys_read+0x45/0x69
> [ 26.756996] [<ffffffff810026eb>] system_call_fastpath+0x16/0x1b
> [ 26.788544] dracut: Switching root
>




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