locking api self-test hanging

locking api self-test hanging

[Andrew Morton]

With current mainline I'm getting intermittent hangs here:

	http://userweb.kernel.org/~akpm/p2033590.jpg

with this config:

	http://userweb.kernel.org/~akpm/config-sony.txt

on the Vaio.  Sometimes it boots (then hits another different hang),
sometimes it gets stuck there.

Re: locking api self-test hanging

[Andrew Morton]

On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> 
> With current mainline I'm getting intermittent hangs here:
> 
> 	http://userweb.kernel.org/~akpm/p2033590.jpg
> 
> with this config:
> 
> 	http://userweb.kernel.org/~akpm/config-sony.txt
> 
> on the Vaio.  Sometimes it boots (then hits another different hang),
> sometimes it gets stuck there.
> 

The second hang is in kobject_uevent_init().  All that function does is call
netlink_kernel_create().

These things make bisecting all the other bugs rather hard.

Re: locking api self-test hanging

[Andrew Morton]

On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > 
> > With current mainline I'm getting intermittent hangs here:
> > 
> > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > 
> > with this config:
> > 
> > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > 
> > on the Vaio.  Sometimes it boots (then hits another different hang),
> > sometimes it gets stuck there.

CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.

> 
> The second hang is in kobject_uevent_init().  All that function does is call
> netlink_kernel_create().

And I've fully bisected this hang twice and both times came up with

commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
Author: Stephen Hemminger <shemminger@linux-foundation.org>
Date:   Mon Nov 19 19:24:52 2007 -0800

    [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.

which is stupid because that patch doesn't do anything.

However I am using netconsole-over-e100 and the hang does go away when I
disable netconsole on the kernel boot command line.

I'd say it's some timing thing in netpoll/netconsole/napi/etc.

Re: locking api self-test hanging

[Andrew Morton]

On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > 
> > > With current mainline I'm getting intermittent hangs here:
> > > 
> > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > 
> > > with this config:
> > > 
> > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > 
> > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > sometimes it gets stuck there.
> 
> CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> 
> > 
> > The second hang is in kobject_uevent_init().  All that function does is call
> > netlink_kernel_create().
> 
> And I've fully bisected this hang twice and both times came up with
> 
> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> Author: Stephen Hemminger <shemminger@linux-foundation.org>
> Date:   Mon Nov 19 19:24:52 2007 -0800
> 
>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> 
> which is stupid because that patch doesn't do anything.
> 
> However I am using netconsole-over-e100 and the hang does go away when I
> disable netconsole on the kernel boot command line.
> 

After disabling both CONFIG_DEBUG_LOCKING_API_SELFTESTS and netconsole
(using current mainline) I get a login prompt, and also...

[    5.181668] SELinux: policy loaded with handle_unknown=deny
[    5.183315] type=1403 audit(1202100038.157:3): policy loaded auid=4294967295 ses=4294967295
[    5.822073] SELinux: initialized (dev usbfs, type usbfs), uses genfs_contexts
[    7.819146] ------------[ cut here ]------------
[    7.819146] WARNING: at kernel/lockdep.c:2033 trace_hardirqs_on+0x9b/0x10d()
[    7.819146] Modules linked in: generic ext3 jbd ide_disk ide_core
[    7.819146] Pid: 399, comm: hwclock Not tainted 2.6.24 #4
[    7.819146]  [<c011d140>] warn_on_slowpath+0x41/0x51
[    7.819146]  [<c01364a9>] ? lock_release_holdtime+0x50/0x56
[    7.819146]  [<c013770c>] ? check_usage_forwards+0x19/0x3b
[    7.819146]  [<c01390c4>] ? __lock_acquire+0xac3/0xb0b
[    7.819146]  [<c0108c98>] ? native_sched_clock+0x8b/0x9f
[    7.819146]  [<c01364a9>] ? lock_release_holdtime+0x50/0x56
[    7.819146]  [<c030ca6c>] ? _spin_unlock_irq+0x22/0x42
[    7.819146]  [<c013848b>] trace_hardirqs_on+0x9b/0x10d
[    7.819146]  [<c030ca6c>] _spin_unlock_irq+0x22/0x42
[    7.819146]  [<c011481e>] hpet_rtc_interrupt+0xdf/0x290
[    7.819146]  [<c014ea90>] handle_IRQ_event+0x1a/0x46
[    7.819146]  [<c014f8ea>] handle_edge_irq+0xbe/0xff
[    7.819146]  [<c0106e08>] do_IRQ+0x6d/0x84
[    7.819146]  [<c0105596>] common_interrupt+0x2e/0x34
[    7.819146]  [<c013007b>] ? ktime_get_ts+0x8/0x3f
[    7.819146]  [<c0139420>] ? lock_release+0x167/0x16f
[    7.819146]  [<c017974a>] ? core_sys_select+0x2c/0x327
[    7.819146]  [<c0179792>] core_sys_select+0x74/0x327
[    7.819146]  [<c0108c98>] ? native_sched_clock+0x8b/0x9f
[    7.819146]  [<c01364a9>] ? lock_release_holdtime+0x50/0x56
[    7.819146]  [<c030ca6c>] ? _spin_unlock_irq+0x22/0x42
[    7.819146]  [<c01384d6>] ? trace_hardirqs_on+0xe6/0x10d
[    7.819146]  [<c030ca77>] ? _spin_unlock_irq+0x2d/0x42
[    7.819146]  [<c023b437>] ? rtc_do_ioctl+0x11b/0x677
[    7.819146]  [<c01c487e>] ? inode_has_perm+0x5e/0x68
[    7.819146]  [<c01364a9>] ? lock_release_holdtime+0x50/0x56
[    7.819146]  [<c0108c98>] ? native_sched_clock+0x8b/0x9f
[    7.819146]  [<c01c490b>] ? file_has_perm+0x83/0x8c
[    7.819146]  [<c023ba08>] ? rtc_ioctl+0xf/0x11
[    7.819146]  [<c017898d>] ? do_ioctl+0x55/0x67
[    7.819146]  [<c0179d15>] sys_select+0x93/0x163
[    7.819146]  [<c0104b39>] ? sysenter_past_esp+0x9a/0xa5
[    7.819146]  [<c0104afe>] sysenter_past_esp+0x5f/0xa5
[    7.819146]  =======================
[    7.819146] ---[ end trace 96540ca301ffb84c ]---
[    7.819210] rtc: lost 6 interrupts
[    7.870668] type=1400 audit(1202128840.794:4): avc:  denied  { audit_write } for  pid=399 comm="hwclock" capability=29 scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:hwclock_t:s0 tclass=capability
[    9.538866] input: PC Speaker as /class/input/input5

Because hpet_rtc_interrupt()'s call to get_rtc_time() ends up
resolving to include/asm-generic/rtc.h's (hilariously inlined)
get_rtc_time(), which does spin_unlock_irq() from hard IRQ context.

That warning in lockdep.c should have a comment explaining to readers under
which circumstances it will trigger, and what they did wrong.  In fact if
I've interpreted it correctly I don't see why it's a DEBUG_LOCKS_WARN_ON
thing at all?  It should be a first-class lockdep warning?

The obvious patch fixes it:

--- a/include/asm-generic/rtc.h~a
+++ a/include/asm-generic/rtc.h
@@ -35,10 +35,11 @@
 static inline unsigned char rtc_is_updating(void)
 {
 	unsigned char uip;
+	unsigned long flags;
 
-	spin_lock_irq(&rtc_lock);
+	spin_lock_irqsave(&rtc_lock, flags);
 	uip = (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP);
-	spin_unlock_irq(&rtc_lock);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 	return uip;
 }
 
@@ -46,6 +47,8 @@ static inline unsigned int get_rtc_time(
 {
 	unsigned long uip_watchdog = jiffies;
 	unsigned char ctrl;
+	unsigned long flags;
+
 #ifdef CONFIG_MACH_DECSTATION
 	unsigned int real_year;
 #endif
@@ -72,7 +75,7 @@ static inline unsigned int get_rtc_time(
 	 * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
 	 * by the RTC when initially set to a non-zero value.
 	 */
-	spin_lock_irq(&rtc_lock);
+	spin_lock_irqsave(&rtc_lock, flags);
 	time->tm_sec = CMOS_READ(RTC_SECONDS);
 	time->tm_min = CMOS_READ(RTC_MINUTES);
 	time->tm_hour = CMOS_READ(RTC_HOURS);
@@ -83,7 +86,7 @@ static inline unsigned int get_rtc_time(
 	real_year = CMOS_READ(RTC_DEC_YEAR);
 #endif
 	ctrl = CMOS_READ(RTC_CONTROL);
-	spin_unlock_irq(&rtc_lock);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	if (!(ctrl & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
 	{
_


but that code really needs help.

Bernhard, I believe the checklist items in Documentation/SubmitChecklist
would have prevented this at the source.


ObProcessObservation: afacit the offending commit went mailing list ->
git-x86 -> mainline in about three days flat, a week after the merge
window had opened.

Re: locking api self-test hanging

[Peter Zijlstra]

On Mon, 2008-02-04 at 05:04 -0800, Andrew Morton wrote:

> After disabling both CONFIG_DEBUG_LOCKING_API_SELFTESTS and netconsole
> (using current mainline) I get a login prompt, and also...

> [    7.819146] WARNING: at kernel/lockdep.c:2033 trace_hardirqs_on+0x9b/0x10d()

> That warning in lockdep.c should have a comment explaining to readers under
> which circumstances it will trigger, and what they did wrong.  In fact if
> I've interpreted it correctly I don't see why it's a DEBUG_LOCKS_WARN_ON
> thing at all?  It should be a first-class lockdep warning?

Agreed, I'll make lockdep print a nice error.

Re: locking api self-test hanging

[Andrew Morton]

On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > 
> > > With current mainline I'm getting intermittent hangs here:
> > > 
> > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > 
> > > with this config:
> > > 
> > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > 
> > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > sometimes it gets stuck there.
> 
> CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> 
> > 
> > The second hang is in kobject_uevent_init().  All that function does is call
> > netlink_kernel_create().
> 
> And I've fully bisected this hang twice and both times came up with
> 
> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> Author: Stephen Hemminger <shemminger@linux-foundation.org>
> Date:   Mon Nov 19 19:24:52 2007 -0800
> 
>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> 
> which is stupid because that patch doesn't do anything.
> 
> However I am using netconsole-over-e100 and the hang does go away when I
> disable netconsole on the kernel boot command line.
> 
> I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> 

I expect the locking API self-tests are innocent - the netconsole lockup
happened to strike during the locking API tests and fooled me.  When I
disabled those tests, the netconsole lockup struck later on.  

Re: locking api self-test hanging

[Bernhard Walle]

* Andrew Morton <akpm@linux-foundation.org> [2008-02-04 14:04]:
> 
> but that code really needs help.

Using spin_lock_irqsave() is what rtc_get_rtc_time() does which was
used before I changed to get_rtc_time() does. So it should be ok. I
missed that difference. However, I agree with you the whole RTC
"emulation" per HPET is a bit unclean. However, I have too little
experience in this code area to come up with a proper redesign. I just
ported it from the old RTC to the new RTC module interface.

> Bernhard, I believe the checklist items in Documentation/SubmitChecklist
> would have prevented this at the source.

Yes. I must admit that I didn't know that document. I used
checkpatch.pl, but that's of course only for coding style. I'll try to
follow the points in SubmitChecklist in future.



        Bernhard

Re: locking api self-test hanging

[Andrew Morton]

On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > 
> > > With current mainline I'm getting intermittent hangs here:
> > > 
> > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > 
> > > with this config:
> > > 
> > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > 
> > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > sometimes it gets stuck there.
> 
> CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> 
> > 
> > The second hang is in kobject_uevent_init().  All that function does is call
> > netlink_kernel_create().
> 
> And I've fully bisected this hang twice and both times came up with
> 
> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> Author: Stephen Hemminger <shemminger@linux-foundation.org>
> Date:   Mon Nov 19 19:24:52 2007 -0800
> 
>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> 
> which is stupid because that patch doesn't do anything.
> 
> However I am using netconsole-over-e100 and the hang does go away when I
> disable netconsole on the kernel boot command line.
> 
> I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> 

I'm seeing this netconsole hang on a second machine now.  Current
mainline.  It also has e100.  This one is SMP ancient PIII.

Config: http://userweb.kernel.org/~akpm/config-vmm.txt

Re: locking api self-test hanging

[Andrew Morton]

On Wed, 6 Feb 2008 00:34:12 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > 
> > > > With current mainline I'm getting intermittent hangs here:
> > > > 
> > > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > > 
> > > > with this config:
> > > > 
> > > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > > 
> > > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > > sometimes it gets stuck there.
> > 
> > CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> > 
> > > 
> > > The second hang is in kobject_uevent_init().  All that function does is call
> > > netlink_kernel_create().
> > 
> > And I've fully bisected this hang twice and both times came up with
> > 
> > commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> > Author: Stephen Hemminger <shemminger@linux-foundation.org>
> > Date:   Mon Nov 19 19:24:52 2007 -0800
> > 
> >     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> > 
> > which is stupid because that patch doesn't do anything.
> > 
> > However I am using netconsole-over-e100 and the hang does go away when I
> > disable netconsole on the kernel boot command line.
> > 
> > I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> > 
> 
> I'm seeing this netconsole hang on a second machine now.  Current
> mainline.  It also has e100.  This one is SMP ancient PIII.
> 
> Config: http://userweb.kernel.org/~akpm/config-vmm.txt
> 

I can reproduce this on a third machine: the t61p laptop: dual x86_64 with
e1000.

It seems to need quite a lot of printk activity to make it happen.  Turning
on initcall_debug is a suitable way of triggering it.

Re: locking api self-test hanging

[Andrew Morton]

On Wed, 6 Feb 2008 01:16:43 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 6 Feb 2008 00:34:12 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > 
> > > > > 
> > > > > With current mainline I'm getting intermittent hangs here:
> > > > > 
> > > > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > > > 
> > > > > with this config:
> > > > > 
> > > > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > > > 
> > > > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > > > sometimes it gets stuck there.
> > > 
> > > CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> > > 
> > > > 
> > > > The second hang is in kobject_uevent_init().  All that function does is call
> > > > netlink_kernel_create().
> > > 
> > > And I've fully bisected this hang twice and both times came up with
> > > 
> > > commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> > > Author: Stephen Hemminger <shemminger@linux-foundation.org>
> > > Date:   Mon Nov 19 19:24:52 2007 -0800
> > > 
> > >     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> > > 
> > > which is stupid because that patch doesn't do anything.
> > > 
> > > However I am using netconsole-over-e100 and the hang does go away when I
> > > disable netconsole on the kernel boot command line.
> > > 
> > > I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> > > 
> > 
> > I'm seeing this netconsole hang on a second machine now.  Current
> > mainline.  It also has e100.  This one is SMP ancient PIII.
> > 
> > Config: http://userweb.kernel.org/~akpm/config-vmm.txt
> > 
> 
> I can reproduce this on a third machine: the t61p laptop: dual x86_64 with
> e1000.
> 
> It seems to need quite a lot of printk activity to make it happen.  Turning
> on initcall_debug is a suitable way of triggering it.
> 

This netconsole regression is still present in current mainline.  Rafael,
can you please add it to the list?

It's strange that I can hit it on three separate machines with e100 and e1000
yet nobody else has reported it (afaik).  Is nobody using netconsole?

[patch] mark netconsole broken

[Ingo Molnar]

* Andrew Morton <akpm@linux-foundation.org> wrote:

> This netconsole regression is still present in current mainline.  
> Rafael, can you please add it to the list?
> 
> It's strange that I can hit it on three separate machines with e100 
> and e1000 yet nobody else has reported it (afaik).  Is nobody using 
> netconsole?

i'd suggest the patch below, to mark it broken.

	Ingo

---
 drivers/net/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux/drivers/net/Kconfig
===================================================================
--- linux.orig/drivers/net/Kconfig
+++ linux/drivers/net/Kconfig
@@ -3109,7 +3109,7 @@ config NET_FC
 
 config NETCONSOLE
 	tristate "Network console logging support (EXPERIMENTAL)"
-	depends on EXPERIMENTAL
+	depends on EXPERIMENTAL && BROKEN
 	---help---
 	If you want to log kernel messages over the network, enable this.
 	See <file:Documentation/networking/netconsole.txt> for details.

Re: locking api self-test hanging

[Jarek Poplawski]

On 04-03-2008 06:05, Andrew Morton wrote:
...
>>>> And I've fully bisected this hang twice and both times came up with
>>>>
>>>> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
>>>> Author: Stephen Hemminger <shemminger@linux-foundation.org>
>>>> Date:   Mon Nov 19 19:24:52 2007 -0800
>>>>
>>>>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
>>>>
>>>> which is stupid because that patch doesn't do anything.

...or maybe apparently doesn't do anything?

@@ -128,13 +127,11 @@ static int poll_one_napi(struct netpoll_info *npinfo,
        if (!test_bit(NAPI_STATE_SCHED, &napi->state))
                return budget;
 
-       npinfo->rx_flags |= NETPOLL_RX_DROP;


But in a next patch we can see:

@@ -51,12 +50,12 @@ static inline int netpoll_rx(struct sk_buff *skb)
        unsigned long flags;
        int ret = 0;
 
-       if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
+       if (!npinfo || !npinfo->rx_np)

So, it seems rx_flags could have been tested here for NETPOLL_RX_DROP
yet?

Regards,
Jarek P.

Re: locking api self-test hanging

[Andrew Morton]

On Tue, 4 Mar 2008 08:40:24 +0000 Jarek Poplawski <jarkao2@gmail.com> wrote:

> On 04-03-2008 06:05, Andrew Morton wrote:
> ...
> >>>> And I've fully bisected this hang twice and both times came up with
> >>>>
> >>>> commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> >>>> Author: Stephen Hemminger <shemminger@linux-foundation.org>
> >>>> Date:   Mon Nov 19 19:24:52 2007 -0800
> >>>>
> >>>>     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> >>>>
> >>>> which is stupid because that patch doesn't do anything.
> 
> ...or maybe apparently doesn't do anything?
> 
> @@ -128,13 +127,11 @@ static int poll_one_napi(struct netpoll_info *npinfo,
>         if (!test_bit(NAPI_STATE_SCHED, &napi->state))
>                 return budget;
>  
> -       npinfo->rx_flags |= NETPOLL_RX_DROP;
> 
> 
> But in a next patch we can see:
> 
> @@ -51,12 +50,12 @@ static inline int netpoll_rx(struct sk_buff *skb)
>         unsigned long flags;
>         int ret = 0;
>  
> -       if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
> +       if (!npinfo || !npinfo->rx_np)
> 
> So, it seems rx_flags could have been tested here for NETPOLL_RX_DROP
> yet?
> 

Oh damn.  I bisected this three times and the second two times both landed on
this:


commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
Author: Stephen Hemminger <shemminger@linux-foundation.org>
Date:   Mon Nov 19 19:24:52 2007 -0800

    [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
    
    Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index cf6acd3..9e3aea0 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -40,7 +40,6 @@ static atomic_t trapped;
 
 #define USEC_PER_POLL	50
 #define NETPOLL_RX_ENABLED  1
-#define NETPOLL_RX_DROP     2
 
 #define MAX_SKB_SIZE \
 		(MAX_UDP_CHUNK + sizeof(struct udphdr) + \
@@ -128,13 +127,11 @@ static int poll_one_napi(struct netpoll_info *npinfo,
 	if (!test_bit(NAPI_STATE_SCHED, &napi->state))
 		return budget;
 
-	npinfo->rx_flags |= NETPOLL_RX_DROP;
 	atomic_inc(&trapped);
 
 	work = napi->poll(napi, budget);
 
 	atomic_dec(&trapped);
-	npinfo->rx_flags &= ~NETPOLL_RX_DROP;
 
 	return budget - work;
 }
@@ -475,7 +472,7 @@ int __netpoll_rx(struct sk_buff *skb)
 	if (skb->dev->type != ARPHRD_ETHER)
 		goto out;
 
-	/* check if netpoll clients need ARP */
+	/* if receive ARP during middle of NAPI poll, then queue */
 	if (skb->protocol == htons(ETH_P_ARP) &&
 	    atomic_read(&trapped)) {
 		skb_queue_tail(&npi->arp_tx, skb);
@@ -537,6 +534,9 @@ int __netpoll_rx(struct sk_buff *skb)
 	return 1;
 
 out:
+	/* If packet received while already in poll then just
+	 * silently drop.
+	 */
 	if (atomic_read(&trapped)) {
 		kfree_skb(skb);
 		return 1;

and I stupidly assumed that it couldn't be this commit because it was a
no-op.  I didn't think to look for an _impicit_ test of NETPOLL_RX_DROP
such as the one above.  That's pretty poor style IMO :(


That bisecting took me several hours and at the time I hoped that it would
receive a more-than-zero response.  btw.

Re: [patch] mark netconsole broken

[Randy Dunlap]

On Tue, 4 Mar 2008 09:06:44 +0100 Ingo Molnar wrote:

> 
> * Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > This netconsole regression is still present in current mainline.  
> > Rafael, can you please add it to the list?
> > 
> > It's strange that I can hit it on three separate machines with e100 
> > and e1000 yet nobody else has reported it (afaik).  Is nobody using 
> > netconsole?

Sorry, I don't read 100% of any mailing list.

I use netconsole on my automated testing systems daily or at
least as often as there is a linus (-git) or -mm release.
It's still working for me, but I'm not using an e100[0] driver,
I'm using a Broadcom.


> i'd suggest the patch below, to mark it broken.
> 
> 	Ingo
> 
> ---
>  drivers/net/Kconfig |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux/drivers/net/Kconfig
> ===================================================================
> --- linux.orig/drivers/net/Kconfig
> +++ linux/drivers/net/Kconfig
> @@ -3109,7 +3109,7 @@ config NET_FC
>  
>  config NETCONSOLE
>  	tristate "Network console logging support (EXPERIMENTAL)"
> -	depends on EXPERIMENTAL
> +	depends on EXPERIMENTAL && BROKEN
>  	---help---
>  	If you want to log kernel messages over the network, enable this.
>  	See <file:Documentation/networking/netconsole.txt> for details.

---
~Randy

Re: locking api self-test hanging

[Marcin Slusarz]

On Mon, Mar 03, 2008 at 09:05:40PM -0800, Andrew Morton wrote:
> On Wed, 6 Feb 2008 01:16:43 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > On Wed, 6 Feb 2008 00:34:12 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > On Mon, 4 Feb 2008 04:43:04 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > 
> > > > On Sun, 3 Feb 2008 15:07:44 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > 
> > > > > On Sun, 3 Feb 2008 15:02:46 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > > 
> > > > > > 
> > > > > > With current mainline I'm getting intermittent hangs here:
> > > > > > 
> > > > > > 	http://userweb.kernel.org/~akpm/p2033590.jpg
> > > > > > 
> > > > > > with this config:
> > > > > > 
> > > > > > 	http://userweb.kernel.org/~akpm/config-sony.txt
> > > > > > 
> > > > > > on the Vaio.  Sometimes it boots (then hits another different hang),
> > > > > > sometimes it gets stuck there.
> > > > 
> > > > CONFIG_DEBUG_LOCKING_API_SELFTESTS=n fixed that up.
> > > > 
> > > > > 
> > > > > The second hang is in kobject_uevent_init().  All that function does is call
> > > > > netlink_kernel_create().
> > > > 
> > > > And I've fully bisected this hang twice and both times came up with
> > > > 
> > > > commit 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7
> > > > Author: Stephen Hemminger <shemminger@linux-foundation.org>
> > > > Date:   Mon Nov 19 19:24:52 2007 -0800
> > > > 
> > > >     [NETPOLL]: Kill NETPOLL_RX_DROP, set but never tested.
> > > > 
> > > > which is stupid because that patch doesn't do anything.
> > > > 
> > > > However I am using netconsole-over-e100 and the hang does go away when I
> > > > disable netconsole on the kernel boot command line.
> > > > 
> > > > I'd say it's some timing thing in netpoll/netconsole/napi/etc.
> > > > 
> > > 
> > > I'm seeing this netconsole hang on a second machine now.  Current
> > > mainline.  It also has e100.  This one is SMP ancient PIII.
> > > 
> > > Config: http://userweb.kernel.org/~akpm/config-vmm.txt
> > > 
> > 
> > I can reproduce this on a third machine: the t61p laptop: dual x86_64 with
> > e1000.
> > 
> > It seems to need quite a lot of printk activity to make it happen.  Turning
> > on initcall_debug is a suitable way of triggering it.
> > 
I've seen it once too. But I thought it had something to do with this:
http://lkml.org/lkml/2008/3/2/91

> This netconsole regression is still present in current mainline.  Rafael,
> can you please add it to the list?
> 
> It's strange that I can hit it on three separate machines with e100 and e1000
> yet nobody else has reported it (afaik).  Is nobody using netconsole?

ps: I don't have any e100* card

Re: [patch] mark netconsole broken

[David Miller]

From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 4 Mar 2008 09:06:44 +0100

> i'd suggest the patch below, to mark it broken.

Why bother when we know what the bug is and can fix it? :-)

commit d9452e9f81e997cbd0c9bface8d2c2a4b064cc3e
Author: David S. Miller <davem@davemloft.net>
Date:   Tue Mar 4 12:28:49 2008 -0800

    [NETPOLL]: Revert two bogus cleanups that broke netconsole.
    
    Based upon a report by Andrew Morton and code analysis done
    by Jarek Poplawski.
    
    This reverts 33f807ba0d9259e7c75c7a2ce8bd2787e5b540c7 ("[NETPOLL]:
    Kill NETPOLL_RX_DROP, set but never tested.")  and
    c7b6ea24b43afb5749cb704e143df19d70e23dea ("[NETPOLL]: Don't need
    rx_flags.").
    
    The rx_flags did get tested for zero vs. non-zero and therefore we do
    need those tests and that code which sets NETPOLL_RX_DROP et al.
    
    Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index a0525a1..e3d7959 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -25,6 +25,7 @@ struct netpoll {
 
 struct netpoll_info {
 	atomic_t refcnt;
+	int rx_flags;
 	spinlock_t rx_lock;
 	struct netpoll *rx_np; /* netpoll that registered an rx_hook */
 	struct sk_buff_head arp_tx; /* list of arp requests to reply to */
@@ -50,12 +51,12 @@ static inline int netpoll_rx(struct sk_buff *skb)
 	unsigned long flags;
 	int ret = 0;
 
-	if (!npinfo || !npinfo->rx_np)
+	if (!npinfo || (!npinfo->rx_np && !npinfo->rx_flags))
 		return 0;
 
 	spin_lock_irqsave(&npinfo->rx_lock, flags);
-	/* check rx_np again with the lock held */
-	if (npinfo->rx_np && __netpoll_rx(skb))
+	/* check rx_flags again with the lock held */
+	if (npinfo->rx_flags && __netpoll_rx(skb))
 		ret = 1;
 	spin_unlock_irqrestore(&npinfo->rx_lock, flags);
 
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 6faa128..4b7e756 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -39,6 +39,8 @@ static struct sk_buff_head skb_pool;
 static atomic_t trapped;
 
 #define USEC_PER_POLL	50
+#define NETPOLL_RX_ENABLED  1
+#define NETPOLL_RX_DROP     2
 
 #define MAX_SKB_SIZE \
 		(MAX_UDP_CHUNK + sizeof(struct udphdr) + \
@@ -126,11 +128,13 @@ static int poll_one_napi(struct netpoll_info *npinfo,
 	if (!test_bit(NAPI_STATE_SCHED, &napi->state))
 		return budget;
 
+	npinfo->rx_flags |= NETPOLL_RX_DROP;
 	atomic_inc(&trapped);
 
 	work = napi->poll(napi, budget);
 
 	atomic_dec(&trapped);
+	npinfo->rx_flags &= ~NETPOLL_RX_DROP;
 
 	return budget - work;
 }
@@ -472,7 +476,7 @@ int __netpoll_rx(struct sk_buff *skb)
 	if (skb->dev->type != ARPHRD_ETHER)
 		goto out;
 
-	/* if receive ARP during middle of NAPI poll, then queue */
+	/* check if netpoll clients need ARP */
 	if (skb->protocol == htons(ETH_P_ARP) &&
 	    atomic_read(&trapped)) {
 		skb_queue_tail(&npi->arp_tx, skb);
@@ -534,9 +538,6 @@ int __netpoll_rx(struct sk_buff *skb)
 	return 1;
 
 out:
-	/* If packet received while already in poll then just
-	 * silently drop.
-	 */
 	if (atomic_read(&trapped)) {
 		kfree_skb(skb);
 		return 1;
@@ -675,6 +676,7 @@ int netpoll_setup(struct netpoll *np)
 			goto release;
 		}
 
+		npinfo->rx_flags = 0;
 		npinfo->rx_np = NULL;
 
 		spin_lock_init(&npinfo->rx_lock);
@@ -756,6 +758,7 @@ int netpoll_setup(struct netpoll *np)
 
 	if (np->rx_hook) {
 		spin_lock_irqsave(&npinfo->rx_lock, flags);
+		npinfo->rx_flags |= NETPOLL_RX_ENABLED;
 		npinfo->rx_np = np;
 		spin_unlock_irqrestore(&npinfo->rx_lock, flags);
 	}
@@ -797,6 +800,7 @@ void netpoll_cleanup(struct netpoll *np)
 			if (npinfo->rx_np == np) {
 				spin_lock_irqsave(&npinfo->rx_lock, flags);
 				npinfo->rx_np = NULL;
+				npinfo->rx_flags &= ~NETPOLL_RX_ENABLED;
 				spin_unlock_irqrestore(&npinfo->rx_lock, flags);
 			}
 

Re: [patch] mark netconsole broken

[Ingo Molnar]

* David Miller <davem@davemloft.net> wrote:

> From: Ingo Molnar <mingo@elte.hu>
> Date: Tue, 4 Mar 2008 09:06:44 +0100
> 
> > i'd suggest the patch below, to mark it broken.
> 
> Why bother when we know what the bug is and can fix it? :-)

music to my ears :-)

	Ingo