Message-ID: <201108111908.32729.tim.sander@hbm.com>
Date:	Thu, 11 Aug 2011 19:08:32 +0200
From:	"Tim Sander" <tim.sander@....com>
To:	"Peter Zijlstra" <peterz@...radead.org>
Cc:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	"linux-rt-users" <linux-rt-users@...r.kernel.org>
Subject: Re: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7

Hi Peter
> > Yes it works for CONFIG_PREEMPT_RTB=y and as you say not for
> > CONFIG_PREEMPT_LL=y.
> > 
> > +++ b/mm/filemap.c
> > @@ -2040,7 +2040,7 @@ size_t iov_iter_copy_from_user_atomic(struct page
> > *page,
> > 
> >         char *kaddr;
> >         size_t copied;
> > 
> > -       BUG_ON(!current->pagefault_disabled);
> > +       BUG_ON(!(in_atomic() || current->pagefault_disabled));
> 
> Ah, I had hoped that bit would have cured the PREEMPT_LL=y config.
As stated in the other mail, it was really PREEMPT_LL=y. I hope my error 
didn't cause you any extra work.

> But let me untangle that posix_cpu_timer stuff first, maybe that's in
> the way.
Which *is* visible by CONFIG_PREEMPT_LL.

I just tested 3.0.1 with rt8 patch + the ones i mailed in this thread
in both configurations. I can confirm that CONFIG_PREEMPT_RTB=y
doesn't show any bugs and CONFIG_PREEMPT_LL shows the following bug:

kernel BUG at kernel/posix-cpu-timers.c:1315!                                                                                                   
Unable to handle kernel NULL pointer dereference at virtual address 00000000                                                                                
pgd = c0004000                                                                                                                                              
[00000000] *pgd=00000000                                                                                                                                    
Internal error: Oops: 817 [#1] PREEMPT                                                                                                                      
Modules linked in: af_packet i2c_imx(+) netx netx_reset dspload fpgaload 
mxc_nand(+) nand nand_ids nand_ecc                                                 
CPU: 0    Not tainted  (3.0.1-pmx-rt8 #2)                                                                                                                   
PC is at __bug+0x24/0x30                                                                                                                                    
LR is at walk_stackframe+0x24/0x40                                                                                                                          
pc : [<c002cbf0>]    lr : [<c002cbb0>]    psr: 60000113                                                                                                     
sp : c782ff40  ip : c782fe28  fp : c782ff4c                                                                                                                 
r10: 00000001  r9 : 00000000  r8 : c78b2180                                                                                                                 
r7 : c030463c  r6 : c782e000  r5 : 00000000  r4 : c78b2180                                                                                                  
r3 : 00000000  r2 : 00000001  r1 : c782fe58  r0 : 00000034                                                                                                  
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel                                                                                         
Control: 00c5387d  Table: 87b84008  DAC: 00000017
Process posixcputmr/0 (pid: 6, stack limit = 0xc782e268)
Stack: (0xc782ff40 to 0xc7830000)
ff40: c782ff8c c782ff50 c005a5c0 c002cbd8 00000000 c782ff54 c782ff54 00000000
ff60: 00000000 c78b2180 00000000 c782e000 c030463c c78b2180 00000000 00000001
ff80: c782ffbc c782ff90 c005a88c c005a594 00000000 c7817f28 00000000 c782ffcc
ffa0: c005a800 00000000 00000000 00000000 c782fff4 c782ffc0 c00570f0 c005a80c
ffc0: c7817f28 00000000 00000000 00000000 c782ffd0 c782ffd0 c7817f28 c0057064
ffe0: c0040868 00000013 00000000 c782fff8 c0040868 c0057070 cccdcd6c ffdec890
Backtrace: 
[<c002cbcc>] (__bug+0x0/0x30) from [<c005a5c0>] 
(__run_posix_cpu_timers+0x38/0x278)
[<c005a588>] (__run_posix_cpu_timers+0x0/0x278) from [<c005a88c>] 
(posix_cpu_timers_thread+0x8c/0x124)
[<c005a800>] (posix_cpu_timers_thread+0x0/0x124) from [<c00570f0>] 
(kthread+0x8c/0x94)
[<c0057064>] (kthread+0x0/0x94) from [<c0040868>] (do_exit+0x0/0x2d8)
 r7:00000013 r6:c0040868 r5:c0057064 r4:c7817f28
Code: e59f0010 e1a01003 eb086b03 e3a03000 (e5833000) 
---[ end trace 09b9f42079c77f6a ]---

Thats enough for me today.

Best regards
Tim

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