linux-stable.git/kernel/printk.c, branch linux-2.6.35.y

printk: Fix wake_up_klogd() vs cpu hotplug

2011-02-06T19:03:40+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 
Signed-off-by: Andi Kleen 
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

2011-02-06T19:03:26+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 
Signed-off-by: Andi Kleen 
LKML-Reference: <20101126120235.406766476@de.ibm.com>
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

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

kdb: core for kgdb back end (2 of 2)

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

This patch contains the hooks and instrumentation into kernel which
live outside the kernel/debug directory, which the kdb core
will call to run commands like lsmod, dmesg, bt etc...

CC: linux-arch@vger.kernel.org
Signed-off-by: Jason Wessel 
Signed-off-by: Martin Hicks

printk: avoid warning when CONFIG_PRINTK is disabled

2010-03-06T19:26:33+00:00

kernel/printk.c:72: warning: `saved_console_loglevel' defined but not used

Signed-off-by: Gustavo F. Padovan 
Cc: Ingo Molnar 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge branch 'next' into for-linus

2010-02-28T22:36:31+00:00

syslog: use defined constants instead of raw numbers

2010-02-04T03:20:41+00:00

Right now the syslog "type" action are just raw numbers which makes
the source difficult to follow.  This patch replaces the raw numbers
with defined constants for some level of sanity.

Signed-off-by: Kees Cook 
Acked-by: John Johansen 
Acked-by: Serge Hallyn 
Signed-off-by: James Morris

syslog: distinguish between /proc/kmsg and syscalls

2010-02-04T03:20:12+00:00

This allows the LSM to distinguish between syslog functions originating
from /proc/kmsg access and direct syscalls.  By default, the commoncaps
will now no longer require CAP_SYS_ADMIN to read an opened /proc/kmsg
file descriptor.  For example the kernel syslog reader can now drop
privileges after opening /proc/kmsg, instead of staying privileged with
CAP_SYS_ADMIN.  MAC systems that implement security_syslog have unchanged
behavior.

Signed-off-by: Kees Cook 
Acked-by: Serge Hallyn 
Acked-by: John Johansen 
Signed-off-by: James Morris

Merge git://git.infradead.org/~dwmw2/mtd-2.6.33

2010-01-24T18:31:34+00:00

* git://git.infradead.org/~dwmw2/mtd-2.6.33:
  mtd: tests: fix read, speed and stress tests on NOR flash
  mtd: Really add ARM pismo support
  kmsg_dump: Dump on crash_kexec as well

kmsg_dump: Dump on crash_kexec as well

2009-12-31T19:45:04+00:00

crash_kexec gets called before kmsg_dump(KMSG_DUMP_OOPS) if
panic_on_oops is set, so the kernel log buffer is not stored
for this case.

This patch adds a KMSG_DUMP_KEXEC dump type which gets called
when crash_kexec() is invoked. To avoid getting double dumps,
the old KMSG_DUMP_PANIC is moved below crash_kexec(). The
mtdoops driver is modified to handle KMSG_DUMP_KEXEC in the
same way as a panic.

Signed-off-by: KOSAKI Motohiro 
Acked-by: Simon Kagstrom 
Signed-off-by: David Woodhouse