linux-toradex.git/kernel/printk.c, branch tegra-12r8-early

Merge branch 'linux-tegra-2.6.36' into android-tegra-2.6.36

2011-01-08T01:20:53+00:00

Conflicts:
	arch/arm/mm/cache-v6.S

Change-Id: I1a2063218dd705a762a40f4a9dfe504ce1a1d491

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

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

kernel: printk: Add non exported function for clearing the log ring buffer

2010-09-30T00:49:24+00:00

Signed-off-by: San Mehat

printk: Fix log_buf_copy termination.

2010-09-30T00:49:21+00:00

If idx was non-zero and the log had wrapped, len did not get truncated
to stop at the last byte written to the log.

Revert "printk: remove unused code from kernel/printk.c"

2010-09-30T00:49:19+00:00

This reverts commit acff181d3574244e651913df77332e897b88bff4.

ARM: Make low-level printk work

2010-09-30T00:49:03+00:00

Makes low-level printk work.

Signed-off-by: Tony Lindgren

gcc-4.6: printk: use stable variable to dump kmsg buffer

2010-08-10T03:45:06+00:00

kmsg_dump takes care to sample the global variables
inside a spinlock, but then goes on to use the same
variables outside the spinlock region too.

Use the correct variable. This will make the race
window smaller.

Found by gcc 4.6's new warnings.

Signed-off-by: Andi Kleen 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: fix delayed messages from CPU hotplug events

2010-08-05T12:25:59+00:00

When a secondary CPU is being brought up, it is not uncommon for
printk() to be invoked when cpu_online(smp_processor_id()) == 0.  The
case that I witnessed personally was on MIPS:

http://lkml.org/lkml/2010/5/30/4

If (can_use_console() == 0), printk() will spool its output to log_buf
and it will be visible in "dmesg", but that output will NOT be echoed to
the console until somebody calls release_console_sem() from a CPU that
is online.  Therefore, the boot time messages from the new CPU can get
stuck in "limbo" for a long time, and might suddenly appear on the
screen when a completely unrelated event (e.g. "eth0: link is down")
occurs.

This patch modifies the console code so that any pending messages are
automatically flushed out to the console whenever a CPU hotplug
operation completes successfully or aborts.

The issue was seen on 2.6.34.

Original patch by Kevin Cernekee with cleanups by akpm and additional fixes
by Santosh Shilimkar.  This patch superseeds
https://patchwork.linux-mips.org/patch/1357/.

Signed-off-by: Kevin Cernekee 
To: 
To: 
To: 
To: 
To: 
Cc: 
Cc: 
Reviewed-by: Paul Mundt 
Signed-off-by: Kevin Cernekee 
Patchwork: https://patchwork.linux-mips.org/patch/1534/
LKML-Reference: 
LKML-Reference: 
Signed-off-by: Ralf Baechle

printk,kdb: capture printk() when in kdb shell

2010-05-21T02:04:27+00:00

Certain calls from the kdb shell will call out to printk(), and any of
these calls should get vectored back to the kdb_printf() so that the
kdb pager and processing can be used, as well as to properly channel
I/O to the polled I/O devices.

CC: Randy Dunlap 
Signed-off-by: Jason Wessel 
Acked-by: Andrew Morton