Re: [ANNOUNCE] 3.0.1-rt8 - Regression to 3.0-rt7

From: Tim Sander
Date: Thu Aug 11 2011 - 13:08:59 EST

Hi Peter
> > Yes it works for CONFIG_PREEMPT_RTB=y and as you say not for
> >
> > +++ 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
[<c002cbcc>] (__bug+0x0/0x30) from [<c005a5c0>]
[<c005a588>] (__run_posix_cpu_timers+0x0/0x278) from [<c005a88c>]
[<c005a800>] (posix_cpu_timers_thread+0x0/0x124) from [<c00570f0>]
[<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

Hottinger Baldwin Messtechnik GmbH, Im Tiefen See 45, 64293 Darmstadt, Germany |

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