linux-toradex.git/kernel, branch v2.6.36.3

posix-cpu-timers: workaround to suppress the problems with mt exec

2011-01-07T21:58:52+00:00

commit e0a70217107e6f9844628120412cb27bb4cea194 upstream.

posix-cpu-timers.c correctly assumes that the dying process does
posix_cpu_timers_exit_group() and removes all !CPUCLOCK_PERTHREAD
timers from signal->cpu_timers list.

But, it also assumes that timer->it.cpu.task is always the group
leader, and thus the dead ->task means the dead thread group.

This is obviously not true after de_thread() changes the leader.
After that almost every posix_cpu_timer_ method has problems.

It is not simple to fix this bug correctly. First of all, I think
that timer->it.cpu should use struct pid instead of task_struct.
Also, the locking should be reworked completely. In particular,
tasklist_lock should not be used at all. This all needs a lot of
nontrivial and hard-to-test changes.

Change __exit_signal() to do posix_cpu_timers_exit_group() when
the old leader dies during exec. This is not the fix, just the
temporary hack to hide the problem for 2.6.37 and stable. IOW,
this is obviously wrong but this is what we currently have anyway:
cpu timers do not work after mt exec.

In theory this change adds another race. The exiting leader can
detach the timers which were attached to the new leader. However,
the window between de_thread() and release_task() is small, we
can pretend that sys_timer_create() was called before de_thread().

Signed-off-by: Oleg Nesterov 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

Sched: fix skip_clock_update optimization

2011-01-07T21:58:51+00:00

commit f26f9aff6aaf67e9a430d16c266f91b13a5bff64 upstream.

idle_balance() drops/retakes rq->lock, leaving the previous task
vulnerable to set_tsk_need_resched().  Clear it after we return
from balancing instead, and in setup_thread_stack() as well, so
no successfully descheduled or never scheduled task has it set.

Need resched confused the skip_clock_update logic, which assumes
that the next call to update_rq_clock() will come nearly immediately
after being set.  Make the optimization robust against the waking
a sleeper before it sucessfully deschedules case by checking that
the current task has not been dequeued before setting the flag,
since it is that useless clock update we're trying to save, and
clear unconditionally in schedule() proper instead of conditionally
in put_prev_task().

Signed-off-by: Mike Galbraith 
Reported-by: Bjoern B. Brandenburg 
Tested-by: Yong Zhang 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <1291802742.1417.9.camel@marge.simson.net>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

watchdog: Improve initialisation error message and documentation

2011-01-07T21:58:43+00:00

commit 551423748a4eba55f2eb0fc250d757986471f187 upstream.

The error message 'NMI watchdog failed to create perf event...'
does not make it clear that this is a fatal error for the
watchdog.  It also currently prints the error value as a
pointer, rather than extracting the error code with PTR_ERR().
Fix that.

Add a note to the description of the 'nowatchdog' kernel
parameter to associate it with this message.

Reported-by: Cesare Leonardi 
Signed-off-by: Ben Hutchings 
Cc: 599368@bugs.debian.org
Cc: 608138@bugs.debian.org
Cc: Don Zickus 
Cc: Frederic Weisbecker 
LKML-Reference: <1294009362.3167.126.camel@localhost>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

fix freeing user_struct in user cache

2011-01-07T21:58:42+00:00

commit 4ef9e11d6867f88951e30db910fa015300e31871 upstream.

When racing on adding into user cache, the new allocated from mm slab
is freed without putting user namespace.

Since the user namespace is already operated by getting, putting has
to be issued.

Signed-off-by: Hillf Danton 
Acked-by: Serge Hallyn 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

tracing: Fix panic when lseek() called on "trace" opened for writing

2011-01-07T21:58:33+00:00

commit 364829b1263b44aa60383824e4c1289d83d78ca7 upstream.

The file_ops struct for the "trace" special file defined llseek as seq_lseek().
However, if the file was opened for writing only, seq_open() was not called,
and the seek would dereference a null pointer, file->private_data.

This patch introduces a new wrapper for seq_lseek() which checks if the file
descriptor is opened for reading first. If not, it does nothing.

Signed-off-by: Slava Pestov 
LKML-Reference: <1290640396-24179-1-git-send-email-slavapestov@google.com>
Signed-off-by: Steven Rostedt 
Signed-off-by: Greg Kroah-Hartman

sched: Cure more NO_HZ load average woes

2011-01-07T21:58:31+00:00

commit 0f004f5a696a9434b7214d0d3cbd0525ee77d428 upstream.

There's a long-running regression that proved difficult to fix and
which is hitting certain people and is rather annoying in its effects.

Damien reported that after 74f5187ac8 (sched: Cure load average vs
NO_HZ woes) his load average is unnaturally high, he also noted that
even with that patch reverted the load avgerage numbers are not
correct.

The problem is that the previous patch only solved half the NO_HZ
problem, it addressed the part of going into NO_HZ mode, not of
comming out of NO_HZ mode. This patch implements that missing half.

When comming out of NO_HZ mode there are two important things to take
care of:

 - Folding the pending idle delta into the global active count.
 - Correctly aging the averages for the idle-duration.

So with this patch the NO_HZ interaction should be complete and
behaviour between CONFIG_NO_HZ=[yn] should be equivalent.

Furthermore, this patch slightly changes the load average computation
by adding a rounding term to the fixed point multiplication.

Reported-by: Damien Wyart 
Reported-by: Tim McGrath 
Tested-by: Damien Wyart 
Tested-by: Orion Poplawski 
Tested-by: Kyle McMartin 
Signed-off-by: Peter Zijlstra 
Cc: Chase Douglas 
LKML-Reference: <1291129145.32004.874.camel@laptop>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

printk: Fix wake_up_klogd() vs cpu hotplug

2011-01-07T21:58:30+00:00

commit 49f4138346b3cec2706adff02658fe27ceb1e46f upstream.

wake_up_klogd() may get called from preemptible context but uses
__raw_get_cpu_var() to write to a per cpu variable. If it gets preempted
between getting the address and writing to it, the cpu in question could be
offline if the process gets scheduled back and hence writes to the per cpu data
of an offline cpu.

This buggy behaviour was introduced with fa33507a "printk: robustify
printk, fix #2" which was supposed to fix a "using smp_processor_id() in
preemptible" warning.

Let's use this_cpu_write() instead which disables preemption and makes sure
that the outlined scenario cannot happen.

Signed-off-by: Heiko Carstens 
Acked-by: Eric Dumazet 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101126124247.GC7023@osiris.boeblingen.de.ibm.com>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

PM / Hibernate: Fix PM_POST_* notification with user-space suspend

2011-01-07T21:58:19+00:00

commit 1497dd1d29c6a53fcd3c80f7ac8d0e0239e7389e upstream.

The user-space hibernation sends a wrong notification after the image
restoration because of thinko for the file flag check.  RDONLY
corresponds to hibernation and WRONLY to restoration, confusingly.

Signed-off-by: Takashi Iwai 
Signed-off-by: Rafael J. Wysocki 
Signed-off-by: Greg Kroah-Hartman

nohz: Fix get_next_timer_interrupt() vs cpu hotplug

2011-01-07T21:58:15+00:00

commit dbd87b5af055a0cc9bba17795c9a2b0d17795389 upstream.

This fixes a bug as seen on 2.6.32 based kernels where timers got
enqueued on offline cpus.

If a cpu goes offline it might still have pending timers. These will
be migrated during CPU_DEAD handling after the cpu is offline.
However while the cpu is going offline it will schedule the idle task
which will then call tick_nohz_stop_sched_tick().

That function in turn will call get_next_timer_intterupt() to figure
out if the tick of the cpu can be stopped or not. If it turns out that
the next tick is just one jiffy off (delta_jiffies == 1)
tick_nohz_stop_sched_tick() incorrectly assumes that the tick should
not stop and takes an early exit and thus it won't update the load
balancer cpu.

Just afterwards the cpu will be killed and the load balancer cpu could
be the offline cpu.

On 2.6.32 based kernel get_nohz_load_balancer() gets called to decide
on which cpu a timer should be enqueued (see __mod_timer()). Which
leads to the possibility that timers get enqueued on an offline cpu.
These will never expire and can cause a system hang.

This has been observed 2.6.32 kernels. On current kernels
__mod_timer() uses get_nohz_timer_target() which doesn't have that
problem. However there might be other problems because of the too
early exit tick_nohz_stop_sched_tick() in case a cpu goes offline.

The easiest and probably safest fix seems to be to let
get_next_timer_interrupt() just lie and let it say there isn't any
pending timer if the current cpu is offline.

I also thought of moving migrate_[hr]timers() from CPU_DEAD to
CPU_DYING, but seeing that there already have been fixes at least in
the hrtimer code in this area I'm afraid that this could add new
subtle bugs.

Signed-off-by: Heiko Carstens 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101201091109.GA8984@osiris.boeblingen.de.ibm.com>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

nohz: Fix printk_needs_cpu() return value on offline cpus

2011-01-07T21:58:15+00:00

commit 61ab25447ad6334a74e32f60efb135a3467223f8 upstream.

This patch fixes a hang observed with 2.6.32 kernels where timers got enqueued
on offline cpus.

printk_needs_cpu() may return 1 if called on offline cpus. When a cpu gets
offlined it schedules the idle process which, before killing its own cpu, will
call tick_nohz_stop_sched_tick(). That function in turn will call
printk_needs_cpu() in order to check if the local tick can be disabled. On
offline cpus this function should naturally return 0 since regardless if the
tick gets disabled or not the cpu will be dead short after. That is besides the
fact that __cpu_disable() should already have made sure that no interrupts on
the offlined cpu will be delivered anyway.

In this case it prevents tick_nohz_stop_sched_tick() to call
select_nohz_load_balancer(). No idea if that really is a problem. However what
made me debug this is that on 2.6.32 the function get_nohz_load_balancer() is
used within __mod_timer() to select a cpu on which a timer gets enqueued. If
printk_needs_cpu() returns 1 then the nohz_load_balancer cpu doesn't get
updated when a cpu gets offlined. It may contain the cpu number of an offline
cpu. In turn timers get enqueued on an offline cpu and not very surprisingly
they never expire and cause system hangs.

This has been observed 2.6.32 kernels. On current kernels __mod_timer() uses
get_nohz_timer_target() which doesn't have that problem. However there might be
other problems because of the too early exit tick_nohz_stop_sched_tick() in
case a cpu goes offline.

Easiest way to fix this is just to test if the current cpu is offline and call
printk_tick() directly which clears the condition.

Alternatively I tried a cpu hotplug notifier which would clear the condition,
however between calling the notifier function and printk_needs_cpu() something
could have called printk() again and the problem is back again. This seems to
be the safest fix.

Signed-off-by: Heiko Carstens 
Signed-off-by: Peter Zijlstra 
LKML-Reference: <20101126120235.406766476@de.ibm.com>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman